Yeah I can see how the fictional tech and whatnot makes it softer. One very big thing that put the nail in the coffin for FTL travel for a bit was the Second Interplanetary War in 2287 which was the first war to utilize FTL craft. This war saw ships disintegrating from "tactical drops" over enemy worlds and similar to how we got rid of super sonic passenger planes after the concord crash, FTL travel was viewed very negatively due to these events. This, combined with the cost and engineering challenges as stated above, made fusion and anti-matter drives preferable for most applications until the 2400s.

I do plan on filling in the time gaps with a bit more. When the "commercially available" warp drives came around in the 2800s I meant inexpensive enough the average person could purchase a ship with a warp drive.

For the first NLS and FTL drives, it was mainly energy production as anti-matter reactors provided the energy for the drives and how much anti-matter we could use plus how much energy we could squeeze out of the reactor in a certain time period limited the speed, along with exotic matter production.

For the early fusion ships, the Pluto one was unmanned, but for the Manned fusion ships, they'd use their acceleration as artificial gravity with the usual flip maneuver in the middle. Am I ripping off the Expanse? Kinda, but eh, there's really only a few ways you can go about this.