I don't know, Oblivion had horse and mounted combat too as a new feature and it didn't really change anything.
Oblivion had horses, but no mounted combat. (Mods added that eventually)
Nor did Skyrim, though it seems this was added in by a patch, eventually. I never noticed :-(
The most famous equine-related new feature of Oblivion was overpriced gaudy horse armour DLCs.
I always find it strange that Japanese developers get no (or a lot less) flak for releasing pretty much the same game over and over compared to the Western developers.
There were other reasons for Oblivion getting flak (dumbed down UI compared to Morrowind, much hyped but woefully under-delivered Radiant AI, -- see: Todd Howard --- etc, etc)
From have a great, easy-to-learn/hard-to-master gameplay + deep worldbuilding formula, and consistently improve on it with each iteration (Sekiro being a test run at something a bit different; too different for some tastes, in fact).
They keep their mouths shut about what they're working on until it's nearly done, and never pretend it's going to cure cancer, so that hype does not turn to disappointment when it doesn't. That's why they they don't get much flak; I don't think it's a Japan thing, specifically. They do what they do with quiet, consistent competency. That's it. What is there for anyone to get mad about?