Despite my recent commentary I sort of managed to solve the case and feel a little embarrassed. Post updated.

Advising self-insert-command may be a way. But with my zero knowledge of elisp I have absolutely no idea how to do that. All my attempts have failed.

So for now this kinda adds to my long list of “Not solved in any reasonable way”.

Good Lord! Thank your for this advice, but I’d rather suffer with what I have than follow advice from this hellish machine.

This way of modal editing is fine when you write source code.

I write texts, articles. Most of the time I spend in Insert mode. And when I press u I see a wall of text disappeared.

Exactly. I probably should have explained it in more detail.