The player in question went through Elf a ways, realized he was in over his head, retreated after an intense conflict. I dunno, that sounds pretty fun and interesting to me.
The difficulty spike between Orc 3/4 and Elf 1/2 is not IMO greater than the spike in difficulty between, say, Lair 4 and Shoals 1, and is definitely lower than the difficulty spike between Dungeon 15 and depths 1.
Certain levels within a branch, certain levels (due to layout, unique spawn, and bad luck), and certain branches are going to be harder than you can handle when you first come across them. This is something the player must learn to recognize and respond to appropriately.
As for "trudging back through orcish mines," there is auto-travel. Any degree of non-linearity is going to require some backtracking, necessarily. (Fortunately the game has features that make this mostly painless.)