To be fair, the show makers can't be held accountable for the fans preconceptions about what they'd theorized must have happened in Federation history. I mean, realistically as you've identified this is the real problem ENT encountered all along: that a lot of things that we'd assumed over the years, but which had never actually been confirmed on-screen, suddenly turned out differently to how we'd all imagined them. It's no wonder fandom found it difficult to overcome that...
But that was the entire problem. The only reason why Series Five was a prequel was because they had run out of ideas for what a Star Trek show should be about. Some UPN suit decided that, "hey, it worked for Star Wars, so let's do it for Star Trek!"...even though the jury's still out on if it actually "worked" for SW. But that's a whole other story.
If you're going to make a prequel to one of the most beloved and popular television shows in history, then you have to do it because you love and honor that show, not because you've just run out of ideas of what to do. That's the mentality of Hollywood at present, producing shitty sequels to hit movies from thirty years ago because no one has an original bone in their bodies (or remaking hit movies with soulless replacements).
In the case of ENT, the executive producer himself
claimed to not have watched TOS. Really? The show you're making a prequel of, you've never seen?
There was all kinds of backstory to the formation of the Federation, whether it was the old FASA roleplaying games, or the licensed Trek novels of the 70's and '80's. Granted none of that was canon, nor were they obligated to follow it, but they could have at least done some research. But the show was never really about being a TOS prequel. It was about being a prequel to TNG and VOY, and not a very good one at that. It was more like a prequel in name only, as most of the scripts, characters, sets, props, ships and aliens could have been used for the 8th season of Voyager. By the time they figured that out, they did a 360 and went completely overboard with the TOS references. But by then it was too late.
King Daniel Into Darkness wrote:
I just tried to enjoy it for what it was - and IMO it was at it's very best when they said "fuck the timeline!"* and did the Xindi mission.
I'll have to take your word for that, since I stopped watching the show halfway through the second season because I thought it was crap, only to resume watching around the fourth.