True, but alot of things that make RDR2 better than AC Odyssey are things that are directly a result of the higher budget and higher man-hours. For instance the horse riding, the level of realism that went into the horses in RDR2 in terms of level of detail and animation quality are directly a result of RDR2 being a AAAA/AAA+ rather than a AAA, they probably had a whole team dedicated to the horses that worked on nothing but the horses for at least a year, AC Odyssey just couldn't compete against RDR2 in terms of horses due to the fact that Rockstar had the budget to throw alot more man-hours into the development of the horses than Ubisoft had. Another for instance would be the much greater variety of flavor dialogue, that comes down to Rockstar spending the money to hire a voice cast of over 1000 actors to provide tons of flavor dialogue for the many NPC's you encounter while exploring the open world. In the end, RDR2 having better graphics than AC Odyssey largely comes down to Rockstar throwing more man-hours behind the development of the latest iteration of the Rage engine than Ubisoft was willing to throw into the development of the latest iteration of their Anvil Next engine, it's rumored that the whole first year of development was spent upgrading the RAGE engine for current gen consoles with ongoing improvements throughout the rest of the development.
Now of course there are things like writing that are better in RDR2 which don't really have anything to do with the increased budget and man-hours, Rockstar just picked a better lead writer for RDR2 than Ubisoft picked for AC Odyssey.
You're right. But there is no reason Ubisoft can't put the same resources in Assassin's Creed as Rockstar did in Red Dead Redemption 2. If Ubisoft stuck to do something similar with the same time and money Odyssey would have been the game to follow Brotherhood, which sold over 10 million and would have sold as well as Red Dead Redemption if it didn't have so many sequels since then as it has 8 games between Odyssey and Brotherhood.
We should not make excuses for these publishers. They charge the same $70 for their games and are hugely successful so they should be held in the same regards when it comes to expected quality. I appreciate Rockstar for investing in their product instead of having games made in production lines. I enjoyed Odyssey but it felt really dated compared to other games I played this year, it was also very bloated and they even reused the soundtrack from Assassin's Creed 2. Stuff like that really puts me off and I bought Odyssey at a discounted price and still think its among the worst games I played this year. Its only better than Far Cry 5 and Octopath Traveller.
I don't really think that Assassin's Creed as a series could be profitable if the games had the budget and man hours that Rockstar games do. GTA V had a $250m development + marketing budget and it is rumored that RDR2's budget was even higher. We don't know the budget for AC Odyssey, but the most recent Assassin's Creed budget we do know, Assassin's Creed 2, was $24m development budget alone (the marketing budget is unknown), while Ubisoft's 2014 released Watch Dogs had a $68m development + marketing budget, so it is likely that the budget for all of Ubisoft's recent AAA's like AC Origins, AC Odyssey, and Far Cry 5, were under $100m. That is a big gap in budget. In order to break even on a $250m budget you need to sell like 6m copies at full price, then you an start making a profit on discount sales. AC games, even at the height of the series popularity, don't really sell enough to make a budget that high viable for Ubisoft. While the higher budget could boost reviews, there is no guarantee that higher reviews would result in higher sales (4, Origins, and Odyssey are some of the highest reviewed in the series, and they still didn't sell as well as 3 did).
Could Ubisoft afford to boost the budget and man-hours for AC some? Yes, with the budget that AC Odyssey likely had, it probably broke even within a few weeks of release, which means that all of it's legs will be profit, and the game has micro-transactions as well which results in even more profit. Ubisoft could probably afford to boost the AC budget by around 30-40%, and give each AC team 4 years to make a game instead of 3 (Origins is the only AC game in the series to get 4 years of development as far as we know). Anything more than that though would be a huge risk. Take-Two was only willing to throw a GTA V tier budget behind RDR2, when they first game only sold 14m lifetime, because Rockstar's GTA V was a massive success, Take-Two was banking on the increased popularity of the Rockstar name boosting the sales of RDR2, and it paid off for them.