Hm. Some of boss pattern variations really feel random to me.
For example, in 1st phase of Stage 2 boss, with those "over crossing" patterns... i can play more or less similar during several attemps, but at times patterns would be more tiresome/uncomfortable (and i'll really struggle with moving through, very often would bump into smth), and and other times more doable (with more "visible" ornaments to "wave together with"). And that was with state-practice, so starting condition was always same.
I don't really understand this guy, lol. Perhaps he really begs player to hyper or bomb

Funnily, I usually don't have as much trouble with his 2nd and 3rd phases (even though "blue bullets spam" can be a labyrinth of misfortune, but usually you finish him off before it gets too tight).
"Personal struggles" is also something that always could be a thing, though. Like, even after playing DOJ for a big time, last (not sure) phase of Stage 1 boss still makes me feel nervous and demands bigger concentration then other phases (and I do not mean the powered-up version of him when you destruct left and right thingies so he goes berserk, no, i just mean vanilla attacks), so I usually try quicken the kill via help of pointblank after the phase where he vomits red burst directed at your "moment before" position.
I was abandoning this lovely game for a while (even though got acknowledged with it just around the time I came to this forum), so over the years I was always "on" and "off", and well... after big pause you always get rusty
So rusty that you start dying just on the 1-1 stupidly, haha. So yeah, ofc, practice makes perfect... but there are also always so called... "walls" that you hit with head, for sure.
For me currently it's stage 3's midboss, I think. I finally became more or less understanding how to get through first half of stage 3 (which was crazy for me for a long time), but that beautiful red machine gives me a fight I haven't mastered yet. Usually I destroy his right hand, and then left hand, and then he does "moving around danmaku" pattern that is more painful for me... Because you need to "step over" bullets while moving meanwhile the whole pattern also rotates around - easy to bump into and "oh no!!!". I see some people try to speedkill him via pointblanking, but when I try that I always fall into trap of "pincer attack" because at the moment left/right hands exlode they somehow give you pretty scary bullets from both sides which i cant escape mor often than not.
Which means yeaaaaah I have so long road ahead it's crazy, but hey why not

It really feels nice when you even overcome some "small" things, despite how sad you might be of not conquering the game "in time". I think I passed through era when I was super frustrated with myself. So I enjoy it when I can.
Sorry this random stuff from my mind is more about DOJ itself but it was kinda a response to previous posts.
In the end, I want to quote Dark Souls...
"don't give up, skeleton!"
=)