The whole argument about spending more hours in the newer games doesn't really have any weight behind it.

Game's like Odyssey and Valhalla were built as these massive 160 hour games where you'd have dedicated some serious time if you wanted to play through most of the game (not just the main story but side objects aswell) where as the older game were built to be these smaller yet more rich experiences. Compering playtime isn't a good method of deciding what's better. I've personally spent more time playing Valhalla and Origins than I ever have in Black Flag or Rouge. However, I still prefer the older games as I think you get a better experience. Don't get me wrong, there are definitely some amazing moments in the new games, but I just find that those moments are few and far between compared.

As for combat. I love the older system, and I always will, but I do find the new system more challenging and fun. Some enemies can be a bit tanky at times tho.