Misao This ain't it chief
You can make mechanics that encourage party play that don't boil down to "Is it dark clawed?" Yes, okay. No, Party Wiped harder than anything.
It comes with no warning, it fucks every class that das DoT, it fucks your entire party. It's not an engaging mechanic, it's just a "dark claw this and let me kill it". That's not party play, that's just having a dark claw slave.
It doesn't make the game harder. It just kills your entire party and forces you to regroup, rebuff, and go again (unless Max Pain is off cd again).
Examples of party play: Villa of deceit where the party has to interact with the 4 lights while the Twisted Goddess is immune to damage (The fact she also has Max Pain fucking sucks).
Aquila where you need to drag the mvp toward the circles while the rest of your team needs to survive
Betelgeuze where you need to tank the mvp and hold it's attention while the team goes kill the boss ads so it can take damage again. Requires Devo/Land protector to not get oneshot be spells. Deaths make the boss immune so the support needs to be extra careful too.
These are team mechanics. Notice how they are very clearly signaled and don't wipe your entire party outright.