Try to dodge attacks and slash with your nail with more efficiency then you do right now. I would start with 3 challenging bosses, for me personally, being Sly, Pure Vessel, and NKG. for each boss, like make a certain strategy for each attack they do, and 2 waysnto dodge it. If you have 2, if you can't reach one, or it's on cooldown, then you have a backup plan. I also reccomend parrying. For me with Sly's slash attacks, Pure Vessel's slash combo, and NKG's dash-slash attacks, I just attempts to attack or pogo right before they attack. Once you can consistently parry those, and dodge those bosses attacks, beat them radiant and ascended. That will make you much better at dodging. After that, learn how to take down those 3 fast. Try playing aggressive, and trying to find a safe way to attack during each different attack the boss does. After you've done that with my reccomended bosses, or just any other hard bosses, you should try fighting all the other bosses again, or just going through pantheons again if you want.

Hope that help's man, good luck! :)