Technology and science evolve exponentially for just 1 species... never mind for over 150 spacefaring FTL capable civilizations who share technology, science, knowledge and resources freely between each other (in late 24th century). Voyager crew created a far more powerful/faster version of Slipstream in 4 months with limited resources. You cannot possibly tell me that the resources that Starfleet has in the Federation would be incapable of creating technology for synthesizing benamite crystals far faster, and prevent their degradation within 2 to 5 years (maybe 10) after Voyager returned and solve the phase variance issue. You do realize using adaptive algorithms and AI in research and development in the real world has been a thing for a VERY long time and that it usually takes those algorithms at least 1000x less time to reach solutions compared to humans (on standard computer systems)? In Trek, they have had the luxury of quantum computing in the 23rd century, and transluminal processing since 24th century (our quantum computer was apparently able to do 2.6 billion years worth of research in just 4 minutes). Transwarp? Voyager went through how many TW conduits and even had a functioning Borg TW coil (and detailed sensor scans of it). Coaxial Warp? It worked... the crew adapted it to the shuttle (only for the writers to never mention the technology again) and even broke through the Transwarp threshold (Which admittedly did end up mutating Paris, but still... the data the shuttle accumulated and the biochemical changes Paris and Janeway underwent were well documented). There are also Thermionic generators (which Voyager crew scanned and probably acquired from Species 8472 during their exchange of technologies), along with Tetrion reactor technology (of which Voyager had some scans from Caretakers array and also after studying the Subspace Catapult technology in order to help Tash repair it). Seriously, even Quantum slipstream Version 1 didn't need benamite crystals but could only be used on Voyager for 1 hr due to quantum stresses to the hull. Seriously, with additional research, it would be likely dead simple to design a deflector system capable of dealing with the Quantum Stresses on existing or upcoming new Starfleet Ships. And also, Starfleet encountered a solid Neutronium hull on the Planet killer in the 23rd century. Studying that thing for 70 odd years would have produced ridiculous advancement in weapons, shields and hull material science alone which would even allow Starfleet to reproduce Neutronium in SOME quantities by late 24th century and merge it with existing materials as a composite already. But no, the writers conveniently forgot about that.
Some things have to be sacrificed for the story. Star Trek has always done that. How many technologies did Kirk and Co. find in TOS that were never mentioned again?
Except that we know all of the things I mentioned are part of canon... they acknowledged it all when showing us the Voyager-J and the fact they had records of USS Discovery (or at least what SF of the 23rd century put in)... and for the large part, this all takes place in the PRIME universe and PRIME timeline (aka, SAME timeline and same universe). 'Escaping continuity' only works if you decide to ignore everything in the history or set the thing where history has little or no significance. In this instance, the history we know of and the technologies introduced (heck, even WITHOUT all those technologies Voyager brought back) would have had a MASSIVE impact on how the future is shaped when you stop to think of the mere baseline: Federation by 24th century is comprised of OVER 150 space faring civilizations that FREELY share science, technology, knowledge and resources between each other. That alone has MASSIVE repercussions for the future of Trek. But they acknowledged Slipstream, and then proceeded to fubar it up with 'no benamite crystals' even though the technology to syntesize them in a few years existed on Voyager... like I said, the writers are BAD at taking pre-established technologies and things from the franchise and extrapolating what MIGHT come out of those things when you also mix and mash what we know from the real world. For example... the technology Humans already had in the mid 22nd century was enough to build Dyson Swarms inside solar systems for virtually unlimited energy inside those systems (heck, our technology was sufficiently advanced in 1980-ies to do that). By the 24th, they could materialize matter from energy itself... the concept of Transwarp was nothing new in the 23rd century, or even much faster Warp velocities that would allow a ship crossing the galaxy (or reaching another) in a fraction of the time compared to what wash shown when one is focused towards such advancements and you apply some COMMON SENSE. There is a TON of things Trek writers could have applied from the real world to portray massively more advanced Federation of the 32nd century compared to what we actually saw (and to be fair, we might still see that in Season 4 and 5 of Discovery because atm we saw very little, but I won't hold my breadth because what little we saw showcased practically FAR LESS than even 100 years worth of advancement... heck, in some cases not even that).
Science on Star Trek was just them using it as magic to get out of any situation or explain something. They just found the closest science-y words to related to that problem, they weren't working out equations to make sure it made sense. That's just what Futurama did.
Technology doesn't advance on its own. It's not like there's this clear line of progression from A to Z that technological innovation must follow. There have to be factors, typically socio-economic ones, to drive people to innovate and improve upon what's already there. Honestly, I can totally see technology kind of stagnating for a good chunk of time. They have warp drive, so they don't need to worry about FTL travel. They have subspace communications, so even without warp drive they can still maintain contact with people on other planets. They have replicators, so they don't need to worry about food or other resource scarcity. Life in the galaxy was pretty sweet. As long as they had dilithium to make things go, why would any of them worried about "advancement"?
There's also the issues caused by large scale emergencies like the Burn or the Dominion War, where developing alternate technologies can be crucial but the available resources are not always comparable to peace time. The available economy gets disrupted in ways and can take a long while to recover afterward, even under optimal circumstances.
At a certain point you can't really advance FTL too much, especially since if you hit warp 10 you turn into a salamander. The changes seen in the 32nd century seems to be more about refining it, similar to how the internal combustion engine is largely the same in function but with minor improvements over the decades.
But you are allowed to open and close their cupboards, rearrange their crockery and chairs, and mess with their car, or pull up their top.
Except we've seen transwarp conduits, slipstream drive, spore drive and artificial wormholes, plus whatever The Traveller did...
Don't forget what Barclay did whizzing the D to the center of the galaxy? Oh the traveller, he and Wesley
Yeah, the transwarp tunnels seem to be full of hazardous debris (maybe since Voyager blew the Borg hub to bits), slipstream drive suffers from its own resource shortage and/or is hardly stable, spore drive has been unique to Discovery ever since, artificial wormholes have been unstable except for the Bajoran one. The only FTL methods we saw that seem reliable originate from extremely evolved civilizations and entities. None of them are viable options for a galaxy spanning society. And for Warp itself, no matter how long any given spacefaring species has been around, they always seem to be on the 24th century Fed level, and not much beyond. That’s true for the Vulcans since hundreds of years or the Dominion’s 1000 year history. Warp drive seems to peak relatively quickly, but stays stable forever. the odd Dilithium burn event aside, of course.
The federation at this point still has only been around a mere millennia. It’s not even close to the level of Iconia, T’Kon or Voth. And most of them have fallen eventually, too.