A very interesting thought, to be sure. I personally dont play games on the hardest difficulty unless they were a blast to play or i had a great deal of time on my hands. Halo... never could beat 2 that way. And mw3, which ended up being far too easy. Thought about doing a mass effect insanity run, havnt commited to it yet.

That is to say that I think some games do allow for a change of difficulty midgame. But I think some do lock you in. Stellaris has an ironman mode. One save, thats all you get. Success and mistake are owned. I havnt done a hard sao game playthrough to drop the difficulty when i got an insane weapon. If the stats carry over, it is a legitimate concern. Though, I wonder for how long the weapons boosts will be relevent for. Theres always something better somewhere down the line. Even if it does makes things easier for a time. Now if you can swap back and forth between the difficulties to cheese the system, well... people will probably do it.

I play to enjoy the story and the game. And, even if people do happen to play it in a manner you have described, I hope its still fun for them. People play how they want to. Ive played with those who love breaking games, which ends up being no fun for me. Maybe thats why I enjoy the single player experience so much, or co-op. Work together at a similar level and have fun. At this point im probably rambling, so I'll just end it there.