Odyssey was released a year too early, that's clear. But see, if you and an entitled crew push an expansion or the entire game in fact to an historical low rating on Steam, it's no wonder they won't sell it as deserved, and they won't be able to turn this around ever. The game is over here, including Horizons. FD clearly made mistakes, but here is the players', and I mean: your responsibility: rejoicing on pushing Odyssey down to the 30ies also meant you killed Elite altogether in the end. If not you, then the gamer next to you, or any member of that enraged and entitled crowd. It makes no difference in the end.
I don't think this holds up.
1) Odyssey was very bad on release.
2) This led to bad reviews, which put people who weren't already in the "sure, I'll pre-order it" set off buying it, so poor sales
3) And sure, this may well lead to Frontier not releasing any further large-scale developments for Elite [1].
But what's the actual alternative scenario here?
2a) To avoid the original 3, everyone agrees either not to review it, or to write positive reviews focusing on the good bits only (while continuing to be critical on the forums, of course, so that Frontier doesn't think they can leave it in it's 4.0.0 state)
3a) With the mostly positive initial reviews, people who hadn't pre-ordered then buy the game a few weeks post-release
4a) They aren't in on the agreement, so they leave a bunch of negative reviews when they discover it barely runs on their PCs, etc. and are perhaps even angrier because no-one told them.
or
3b) People who hadn't pre-ordered the game note that it's bad but there's widespread agreement to give Frontier a chance to fix it, ignore the positive reviews, and wander off again rather than buying it in its first year.
The result is the same whichever way: Odyssey doesn't sell well, Frontier spend the next year trying to fix it up (failing entirely on consoles), the
recent reviews are still on the negative side of Mixed after most of a year's effort (they've improved from 32% on release to 42% in the last month, so another two years to get into Mostly Positive?) and presumably anyone buying it now having a fair idea of what they're getting into and already substantially lowered expectations from the initial pre-release hype.
It's not the reviews which are causing poor sales here. (And no, none of them are mine, I'm not on Steam)
[1] That said, there'd be no point in them announcing Odyssey was cancelled on consoles, in the terms they did, if they didn't intend at the moment to at least support and develop it further on PC. So I don't think it's as doomed as you think it is yet - they'll have "one more go", at least, at fixing it.