So, what is an acceptable criticism? When do we have a legitimacy to say that something should change, and when is it not the case?
Honestly, all criticism is permissible I think. The freedom of a creator to do as they see fit only makes sense in world where others have the same freedom to present critique, offer better alternatives or completely disregard the work altogether.
The only thing I'd contest (and it's a bit nit-picky) is the implication that there's a time at which something
should change. The creator's freedom - unless it's doing harm to another - is sacred insofar as they should never be compelled to change anything unless they see good reason. That isn't to say a creator should never change their mind, or on-board sensible feedback (a good creator learns as they go), it's simply that they should never be pressured into doing so.
Personally, I couldn't get along with Sekiro; I tried it, played a good few hours and hit a point where I realised it wasn't for me. I have my criticisms, but I wouldn't necessary expect the developer to change it for me and, honestly, I'm not sure they should. As it stands, it's an interesting, relatively unique experiment in the modern space. Its major successes, its uncompromising design and its many imperfections serve to stimulate interesting conversation about the medium and I think there's massive value in that.
I feel the same way about Breath of the Wild, The Witcher III and RDR2 - none are perfect and even their most ardent champions would have things they'd like to see tweaked and revised if not completely changed.
I can understand the frustration of having a love-hate relationship with a game (I get it often enough) and the temptation to say that if enough people feel strongly about an aspect that it should be changed. But then another part of me (the artist and the writer) says "no, imperfections have their own reason to exist." I know there are special exceptions with games, that certain decisions can completely exclude certain people from enjoying them, but then you get this with films too with people who are particularly sensitive to violence, for example - I wouldn't tell a film director they need to take out the violence, so everyone can enjoy it, and I wouldn't necessarily want to say the same to FromSoft about difficulty in their games.
I'm sure at this stage Miyazaki is aware that his attitude to difficulty limits the broader appeal his games might have and I can only assume that he - and those who employ him - have decided that it's a worthwhile compromise, because - across three different publishers in four years - the games have arguably gotten harder.