I'm trying to figure out what the point would be...

Why would the bad guy have only himself and boss mobs in the dungeon rather than a ton of minions to stop people?

Short answer is... he wouldn't.

He'd throw an army in the way to stop you from getting to him. While I'm sure there's some bad guys who would have a lair where there's a bunch of deadly traps or random teleports to various locations into a Dragons lair for example, but for the most part, they're going to throw their army of minions at you...

So its not like that mechanic is going to change much.

Besides... if some people are having a ton of trouble getting through the current mechanics