Even with alternatives, warp drive may still be the most common and relatively easy to mass produce form of FTL travel, IMO. The alternative propulsion systems may require more rare and exotic materials than dilithium possibly. If anything, the Burn showed that the Federation was not all-mighty and and nowhere near invincible.
Here's the thing, its 800-930 years after encountering those technologies.
No material could possibly remain 'exotic' (none of the technology encountered really used any exotic materials - some like Quantum Slipstream used benamite crystals which were INITIALLY said they COULD take years to make more) indefinitely.
What DISCO writers effectively did was handwawed away all of the technologies for the purpose of drama - aka, lazy storytelling to make the Burn more 'convincing' and DISCO relevant (again, 'lazy writing').
Also, DISCO writers seemingly cannot make up their minds on what it is they were triying to say.
They kept going about Dilithium exploding and how other methods of propulsion never worked... but even IF Dilithium is used for power generation (which initially it didn't - it simply refgulated M/AM reactions), achieving Warp speeds should be independent of the power source you use (aka, you simply need strong enough power source).
DISCO made it seem like every method of propulsion used its own unique power source... which is of course not accurate.
Quantum Slipstream (when it was first encountered on the fake Dauntless) apparently didn't use Antimatter at all (per the dialogue).
The Borg use Transwarp and 'unknown' method of power generation (nothing was said that they use dilithium and M/AM reactors).
The Romulans also used Forced Quantum Singularity as a power source in the late 24th century (no need for dilithium here).
So, a method of FTL propulsion is NOT intricately dependent on one power source or another... you simply need powerful enough energy source (which is the main problem of DISCO's Burn premise - aka, Dilithium was used as a power source, shortages ensued - despite the fact Dilithium recrystalisation tech existed since the late 23rd century - and then it suddenly blew up thanks to a downed UFP ship which had a sole Kelpien child that developed a mental connection between himself and the dilithium around him).
Starfleet encountered different (and more advanced/efficienct/more powerful) energy sources in 23rd and 24th centuries and had detailed scans of all of them.
UFP was even researching new power sources in the late 24th century by itself (Kriega Waves for one thing - the research of which actually SURVIVED).
To think M/AM and dilithium would still be used nearly 1000 years later is absurd - especially when we take into account the problem of dilithium mining and eventual shortages that would ensue, or the fact that technology and science evolve exponentially and SF/UFP would have conceivably stop using M/AM and Dilithium just after the late 24th century.
Then it also ignores most of the technology UFP actually has... such as replicators, highly adaptive computer algorithms that can do R&D themselves in a split second or hours at most, transporters, and of course programmable matter.
Neither of which are ever used to their fullest potential... even though they can easily be used to whip up NEW power sources almost instantly.
In fact, the UFP using M/AM and Dilithium predominantly (alongside fusion) didn't make sense... those would be fairly basic technologies for spacefaring organisations... so, to think that NONE of the UFP species invented anything better is ridiculous.
Methods of propulsion... SF encountered a whole lot of them too... even Benamite crystals would NOT potentially take years to make more of over time because the more you study and use said technology, the process of improving methods of production for those technologies would also advance over time.
In mere 10 to 50 years after using Quantum Slipstream, it wouldn't take them years continuously to continue making new crystals.
They'd also invent a method to slow down the degradation of the said crystals or even recrystalize them (like they do with Dilithium).
Most of what DISCO did was just handwaving for the purpose of drama... nothing more and nothing less.
They should have created a more advanced future and have DISCO find itself on the side where its an antique instead would SF would have had to find relevance for the ship and its crew... more out of pity and as a 'thank you' for saving all life in the galaxy.