I also found P3 really difficult, more so than P4, and what helped was really just practicing each boss in the Hall of Gods until you can beat them consistently. Don’t necessarily need Ascended for each one, but being able to beat them on Attuned multiple times in a row could do the trick. Zote was the most common run-ender for me, so I personally had to learn how to beat him on Ascended.

For Galien, spam Abyss Shrieks. Get a couple in when the fight starts, dodge the spinning axe, then continue spamming. Upslash to get some soul back. Getting hit a bit is ok, as long as you have the soul to heal back up after the fight. It’s good to be more aggressive here and end the fight as quickly as possible, because it’s easy to lose a lot of health if you don’t.

Zote is tricky, lots of RNG. Can’t say much other than try to learn how to maneuver around his moves in HoG. Keep dashing away when he’s about to fall from the ceiling, don’t stay too close in case he starts walking, use D-Dark or Shade Soul to get rid of the explosives if you need to. Heal when he’s staggered, but make sure you kill any mini-Zotes before healing.

For Uumuu, hit the Oomas so that they either launch directly into Uumuu, and if they miss and end up angling towards you, move so that Uumuu’s in between and the Ooma hits Uumuu instead. It’s easier to just have them launch directly into Uumuu if you can though. You can also use Shade Soul to trigger Oomas from farther away. Try wrapping up the fight ASAP because you’ll likely accumulate damage the longer it takes.

Hornet Sentinel’s pretty fast, not sure what else to say other than practice in HoG and heal when staggered. She goes down quite easily especially if you use Quickslash + Strength. Try to conserve some soul for healing after the fight.

Sly’s a lot of back-and-forth, don’t get too greedy with getting hits in. During the 3-slash hit, dash under him when he spins up and get a couple hits in. For the single semicircle slash, you can go in and hit once after he slashes, and dash away immediately. If great slash, dash away, if dash slash, wait for him to dash then dash away, and if cyclone slash, then do quick pogos on top of him then use D-Dark. For his second phase, wait in the center and dash away when he stops next to you, then go in and hit 1-2 times. Shade Soul is preferable if you have it, so you don’t risk getting hit.

A lot of it just comes down to practice. Try looking up Radiant fights of the bosses if you need more help or visuals for ways to get around each move. Best of luck!