Path of Pain is not necessary for 112%, and neither is the Pantheon of Hallownest (though an achievement is locked behind it). You do need to beat the Pantheon of the Knight, however, which I found extremely challenging. Just getting to the final boss of it is difficult enough (though thankfully it's not ascended Markoth lol).
With the Pantheons it is simply practice makes perfect. I managed to "just" beat all the bosses in hollow knight, more or less, with the feeling that I was able to scrape by the difficult ones only just. There was no mastery there but 'good enough' victories. However, the Pantheons demand from you nothing less than mastery over every single boss in the sequence; you cannot just beat a boss, but have to be able to do it consistently. For this you should practice in the Hall of Gods, which allows you to test your skills against any boss you've previously encountered in a pantheon (including ones you have fought but not killed). Don't endlessly throw yourself up against the Pantheons if you're struggling; it'll just demoralize you. Instead identify with who you're having a hard time against and practice in the Hall of Gods until you feel comfortable.
I recommend that if you're having trouble beating a boss, try to beat them on their attuned (normal) form. Then beat them at least 2-3 more times in a sequence. Then, if you're feeling confident, try to beat them on ascended form (double mask damage and some bosses have new platforms and forms). If you find ascended form too difficult, that's okay; beat them a few more times on attuned form. Personally, once I have beaten a boss on ascended form I have comfortably mastered or at least begun to intuitively understand their movement. You will develop a muscle memory along with certain tricks that make particular bosses much easier.
Personally, when I hit a roadblock in the Hall of Gods, with the Pantheon of the Sage, I replayed the whole game. I was shocked by how much better I already was and how bosses which gave me such a headache were cleaved through without a thought. Then, I had a torturous time with the Pantheon of the Knight, and committed to defeating Pure Vessel consistently in the Hall of Gods. It was very tough, but after a whole lot of tries, I figured out a particular cycle of healing (you can heal two masks without quick focus if you time it right every stagger) and settled on a particular build which worked for me (sharp shadow+unbreakable strength+quickslash+mark of pride).
Then, after a hellish series of failures, I was finally able to defeat Pure Vessel and claim the 112%. I vowed I was done with the game but actually came back to try the Pantheon of Hallownest. That took me many more tries, practice with some specific toughies (including some of the surprises the fifth pantheon throws at you), and doing the entire game again 100% on Steel Soul. But I was finally able to defeat the whole pantheon, despite only a few weeks earlier complaining that soul warrior was too hard and I was incapable of progressing past soul sanctum.
All it took was a lot of practice and knowing when to stop. If I was really unable to do something (like the path of pain, which I failed several times and only successfully finished after my steel soul run) I acknowledged my skill level was not there and either practiced, replayed the game, or did something else. But if you do manage to break through all the way to the end, you'll hopefully have the same joy of technical mastery that I've rarely gotten with most games because I've never been able to master the mechanics of a game quite like I did Hollow Knight.
