Potentially. But there is no basis for comparison. Mind you, Voyager was more powerful than the borg for all intents and purposes toward the end of the series, so that in mind, I wouldn't be surprised if the pakleds could have beaten them if the story required...
The Voth probably had the technology to avoid the Borg, but in a fight they would have eventually adapted and Borgified the Voth. It is inevitable!
The Borg can't adapt to everything. They are species out there whose weapons are just so much stronger than Borg shields that they can't adapt and will ALWAYS takes damage from them.
Is it inevitable though? The Borg weren't able to assimilate species 8472, mostly down to their dna, but also, largely due to their super-duper-wonder-magic-blow-up-planet-guns. the Voth, while, they will likely be perfectly accepting of borg nano-probes on a genetic level, will probably also have some super-duper-wonder-magic guns of their own that, if detected, they could use to blow the Borgs cyber-gonads off. They're millions of years ahead of anyone else in the galaxy.
They don't hold a candle to the Naceen or the Prophets. The Krenium could erase them without even a face to face confrontation.
the prophets? miles was on the brink of destroying the whole bunch with a beam of sorts, and the founders on the other end will eventually figure out how to get rid of them as well. the krenim never invent their time gun. the voth were not millions of years ahead of the federation, maybe a century or two technologically. for all we know the city ship might be the only one of it's kind, it's size can sustain a population of many millions, and a civilization not based on planets could be that small. the borg had thousands of planets, and tens of thousands of cubes. the drones numbered in the what, quadrillions? their resources are infinitely greater, their progress faster. i think the voth avoided the borg with their cloaking technology, and their ship can outrun the cubes, and the borg might also not care about assimilating the voth because as sauropods, they are too different. even their technology might be undesirable for the borg, they have their transwarp network to places all over the galaxy, and why cloaking if you are the scariest predator anyway? coincidentally, syfy aired the tng episode with hugh today. what a nice, sad, melancholic, compassionate, and tame borg. "but geordie doesn't want to be assimilated". the demotion of the borg started long before voyager, and the voy borg were a lot scarier than the ones of tng.
We don't know how powerful the Voth were, just that they have a "City-Ship". We don't even know if that was the only one. The Borg's numbers don't mean jack sh*t. 10,000 normal people can't hurt Superman.
Miles, the Founders and the Krenuim not inventing a time gun has nothing to do with whether the Voth and more powerful than the Borg. "Unimatrix Zero" explains that the Krenium in general are temporal scientists. They tell us some Krenium were assimilated and the Borg gained the knowledge of temporal machanics.
they can cloak their huge ship, the small ones, and their people. their transwarp is the fastes in open space. their sensors can dedect a ship 100ly away, including sort and number of lifeforms aboard. they can teleport a ship the size of voyager into their cargo hold, and probably anything that physically fits in the space. they are able to hijack an alien ship by overriding or disabling its computers. most impressing, when janeway happily advices the voth to hold onto something because a hole is about to appear in the walls of the city ship, he folds his arms, looks stern, and nothing happens. transmitting the information and disabling the torpedo is quite a technological accomplishment. i guess their ideology also points to a single ship, would be difficult to maintain on several, independently operating ships. superman and q are a different category, gods. we don't know what makes them so powerful. everybody else depends on technology, and first of all, quantity. if numbers didn't matter, germany would have won ww2.
Just because the Nazi's had help from that evil scientist from the Battlestar Galactica that is no reason to put them on a pedestal. I remember a friend ranting once (which hardly makes it a fact) about how germany built these super cool (jet?) fighters inthe last days of the war that could beat the shit out of anything the Allies had to offer, it would probably take dozens of propellor driven planes working in perfect unison/coordination to rought one of these puppies... Hitler took one look at it and said "Excellent, make it a bomber. We must destroy more of England further inland rather than worry about the fingle fighters over the channel." Which of course cut it's speed down to the point that even biplanes from WW1 could bitch slap it. This is what happens when you put a civilian in charge of the military. (Although, Churchill was the stupid bastard who began open season on civilian regions, in favour of the surgical strikes on military targets which had been the common practice until the English got desperate in the face of certain defeat.) the Voth can turn invisible. The Borg don't understand the technology so they can't look for it until after they've assimilated a bit of it and they can't assimilate it until after it turns visible... I suppose they could just randomly carpet bomb space until they found some Voth? Loop hole.
Voyager and her crew were outmatched in every single way against the Voth. Their ship was disabled and they didn't know it, all their tech was rendered inert, etc. etc. Whenever Voyager fights a Cube, she at least has a chance to do some damage with torpedoes, pull off a technobabble escape, try an improvised program, etc etc. None of those worked at on on the Voth, simply because they merely shut the ship down like that. The Borg never did that with the E-D, Voyager, the Saratoga, etc.
Just because the Borg never showed a capability, doesn't mean they lack it. Keep in mind that the Borg learn as much as they can about a species through assimilation and subsequently adaptation. Perhaps, shutting down a ship a ship 'a la the Voth' isn't their tactic. Instead, they prefer gathering information on a vessel and it's capabilities as it runs at it's maximum potential. Sure, it might be 'safer' to disable a ship and then assimilate it, but, the Borg aren't really that obsessed with safety. As for the question if the Voth were more powerful than the Borg... Well, it's possible they were for a time, but their technological level might not be too high in contrast to the Feds. Possibly within a range of 50 to 100 years, maybe more. When you take into consideration 'the Doctrine' (and the stagnation it introduced into Voth society overall - as was explained in the episode), it's entirely possible they haven't really progressed that far at all and the Borg would still come out on top. Actually, it's possible the Borg would be able to beat the Voth with some effort because they are one of the most technologically advanced species in the Galaxy.
Oh, it's possible certainly, but not inevitable as has been stated. We know very little about the Voths capabilities, but what we have seen, has shown them to pretty 'ard.