I just have a few skill suggestions that i can think of other than the normal just git gud retort people usually throw out.
1. Merger of Heaven's Flame and Glacial Spike. Would save time debuffing so say a cleric doesnt have to debuff bosses with their seals. My idea would be like the other merger skills adding the damage together and both weapon get the debuffs of both skills but. Say demon version for axes would make both last 9 seconds or up it to 10 or something and pole use of it just gives critical + debuffs for 6 or 7 seconds. Cant say much for sage since I dont like sage bm skills so i don't play one to remember why I dont like them.
2. Upgraded version of Assassin's Chill of the Deep. Doesnt have to be more powerful just let the buff last for 30 minutes to an hour. Gets annoying when you're farming and buff disappears midboss somewhere lol.
3. Merger skill for Veno's Soul Degen + Amp dmg. ALso to save time for farmers so they can just get into the dd. Make it universal so both demon and sage gets the sage degen's effect and have the amp be alittle stronger than their respective demon/sage version.
I'm sure I could think of others, but this seems to be the only thing that comes to mind.