Barren Realms MUD

okay, this still isn't quite crystallizing for me.

does level difference have any direct influence on outcomes in combat?

or does it only affect things indirectly by determining a mob's base hitroll, ac, and save vs spell/disarm?

A number of things are still level-adjusted. You hit on the major ones of these in save vs. spell and save vs. attribute. Also, of course most spell damage is level adjusted. The amount of damage mobs deal is based in part on their level.

The rest of combat is solely indirectly that level affects it. In that higher leveled mobs have more hp, have lower acs, and have a better to-hit chance. Note that that chance isn't reflected directly in their hitroll, but is based off of behind-the-scenes calculations to-hit.