In Game DPS Meter

[Gormogon]

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Now that's a good idea yet the potential to still be used to deny players is there especially if has a time attack or survival mode. Personally it should still be solo focus that way you can't blame anyone else for failing at situational awareness which helps a player grow individually.

It should just be a "training" tool and players can gauge how well they can handle mechanics and implement what they learn as they go.

Each should be role specific and job specific. Since tanks and healers can still dps some melee can dps/kite, and casters can heal, sleep, kite, etc.

Entry level should focus on utility. Such as slows, stuns, and pushback. Then with ranks that introduce things like AoE's avoidance.
Mid level focuses more on optimizing yourself well. Then with ranks have a random generator for mechanics so you can be in your toes.
High level focuses on being on your best shape and do the mechanics. Kind of what like you can expect with most lvl 50 dungeon bosses and primals.
Expert level might as well basically make solo training version for coil bosses so players can train themselves on the mechanics on said encounters and their rotation so players can know what to do and when.

Yet you can only unlock a coil boss version after you've at least attempted it once.