I've been playing from day one release of Elite Vanilla, So I can give somewhat of a good insight for you.
The game has change so much from the beginning and has always seemed to get better as content is added. Now Odyssey fell flat on its face, literally. But Frontier has picked up the pieces and moved forward, sadly without Console support but Consoles where never meant to be included from the beginning. As an extremely powerful custom-built PC I have to give Frontier true respect for trying to include Consoles and this is not to say that they might not give up on Consoles in the future.
Horizons and Odyssey? It is truly hard to say because the two are already mixed together. Horizons lost quite a few concepts that were very nice via seeding, more random aspects planet-side and seamless play, but that can't be said without giving Odyssey it's due credit in replacing quite a bit of Horizons content with quite a bit of nice details and options. Sadly, the biggest drawback with Odyssey was the loss of seamless play but it's hardly a game breaker.
Odyssey, in my opinion, is in fact a good and bad addition. I really would like to see Frontier Development return to its intended direction as a space flight simulator, but Odyssey has proven to add some new content to bring with Frontiers Developments original direction. Odyssey is done. It can't be taken back nor should it. Horizons and Odyssey are in fact quite the perfect match to move forward with. The two open up an entire new outlook to what Frontier Development can do with two successful engines.
In conclusion, yes, Odyssey deserves its place when optimized properly and bugs fixed. Odyssey was released in a type of Alpha state but polished correctly it could easily have been considered welcomed DLC as Horizons was welcomed.
I am looking forward to seeing what Frontier Development will do with the mix of both Horizons and Odyssey.