Banging my head on wall re: impulse as "power" generation, a field drive, or a FTL system, or making sense of 'simple impulse', or trying to make sense of 'the first warp drive actually being an impulse drive.'
I'd agree that it seems like the FIRST warp drive of ZC could or should have been powered by a fusion reactor, and that a matter-anti-matter reactor with dilithium was a generation or two later (hardware generations...not people generations).
And maybe these fusion reactors on starships can make the impulse engines go darn near lightspeed, or maybe beyond if there is some field-trickery going on... but the 'power'/'electricity' components are seperate than the 'makes it go' components ---even if they're next to eachother. You can have working fusion power with a broken 'thrust' part. If your reactor isn't in your naccelle, you can still have matter/anti-matter reactor power even if your spacewarp coils are eaten up by space bugs.
In my opinion, the most annoying thing about TNG-Treknology was "warp core". Cause, really, it does more than power the warp drive. And there's no spacewarp happening in that 'core'. Just lots of jiggowatts.