LAMs were also verbotten for a lot of that time and they are not a core part of specific faction's forces.
And protos are core for hells horses, snow ravens, a couple homeworld clans, and that is about it. Jade falcons don't use them, ghost bear don't have ASF genotypes and I don't think use them, leaving the wolves the first tier clan that might use them significantly.
You can't play late-jihad WOBbies properly without cybernetics. Can't play proper society without iATM and nova, can't play republic first line units without a bunch of IO level stuff. Can't play Klondike, Age of War or 3040s without prototype level gear. Are you going to suggest that stuff should be core rules? Because if so, you better have a heck of an argument. I view it as another book purchase being a tax on choosing some factions. Not nice, not fair, but little in life is.
The ONLY reason I can see C3 being turned 'off' is if you are facing someone who has ARAD ammo and you do not want to take hits before you are in useful range but since ARAD is advanced rules, like turning equipment off, I am not sure it matters.
Maybe not 'turned off', but brought down by ECM.
As for the fiction, I want it kept in. The wealth of the backstory is one of battletech's strengths, however little some people care for it. The three pages per chapter in the current TW version is a little excessive, however, and a couple of them, notably the protomech one, are a little tangential to the topic at hand. A page per chapter sounds right to me.
Of course, it might not matter, as neither BMM or CampOps have any fiction in them. This suggests to me that the chapter entries have been eliminated, which I think a shame.
Full colour glossy is maybe not necessary. B&W plain paper with a gloss section was fine for FASA, don't see why it wouldn't work now. Although I don't know what the price point difference would be in the modern market. If it's less than $5 or so, there wouldn't be enough benefit.
Backing mechs up hills - another optional rule I think should be optional TW II