Two issues with no magic items:
Certain types of combat get really weird if no one has magic items, which really encourages specific archetypes. Aka ranged PCs over melee. Flying opponents as an example.

A striker PC ought to be averaging about 20/40/60 damage per round at levels 10/20/30 as a baseline. If they're doing that, they kill a standard in the same and 'right' amount of time at all levels. More than that and the DM has to start leveling up encounters to present the right amount of threat, less than that and combats will start to drag out and go with at-wills. The second eventually happens without magic items.