Yeah, buried on Earth and possessing a techbase way beyond that of any known species. The Enterprise struggled to maintain warp 5 and those cyber-zombies managed to upgrade a slower ship to be almost on par with that all by themselves. If Starfleet wasn't run by morons (and written by Beavis and Butthead) they should have been all over that tech and tried to replicate it. As you might have noticed, by then Earth was way beneath all other major starfaring powers in strength, especially the Klingons who were hostile on almost every encounter Enterprise had with them and known as bloodthirsty conquerors to boot (o yeah, and somehow living next door as well).
The only notable aspects about it are that they were buried on Earth (and even then, they're not the only group of alien time travellers to turn up on Earth) and as I recall some drunken ramblings about them by Cochrane, which might have been discounted as too vague or unreliable.
You can try and keep ignoring that the Enterprise had intact Borg tech on board at the end of the episode, but it won't help you. One scan of the Borg cube at J25 and one look into the databank should have told them that this isn't a "first contact".
In that context, Picard's ignorance is quite believable.
Picard's ignorance is unforgivable in fact although that's not just ENT's fault. He was good friends with Guinan and she never told them about the cyber-zombies that blew her homeworld up? Bullshit.
In any case, their are far stupider and more nonsensical things in Star Trek canon (Threshold, various time travel stories, etc.), so focusing on this seems a bit odd. Was it the greatest episode ever? No. But it doesn't deserve the level of hostility you apparently have for it.
What has the existence of worse Trek episodes to do with the fact that Regeneration was clumsily written? Nothing, that's what.