There's some floor modifiers on Tower of Trials which forces a single damage type to be used, magic, ranged or melee.
This can introduce some interesting logistical challenges, mainly if you have ranged against pneuma mobs, or magic against mobs which can use magic mirror; or in general if you roll melee.
However since you're losing 2/3rds of the dps in your party, these floors take agonizingly long to kill compared to all-dps floors to the point of being sleep inducing.
To alleviate this, I believe monsters should have a 66% health reduction on single-damage-type floor modifiers
For example instead of a monster having 200b effective HP on a melee only ToT floor, they would have 66b effective HP instead.
I don't think this would make the floors significantly easier since you'd still have the same logistical challenges mechanically to overcome, and you'll still need good gear to dps the monsters down; but it would happen within a more reasonable timespan for everyone involved.