I totally agree, WoW's leveling is a joke at the moment. In SWTOR pulling even 2 groups of mobs is very risky, and fighting two mobs labeled as "strong" of your level is generally pointless. And 2x heroics are very challenging to solo. In terms of difficulty, I find SWTOR quite satisfactory. However the difficulty is still not as high as for me to stay focused all the time and to really follow enemies' movements to react appropriately (but, I guess, all MMOs are like that these days). WoW breaks this monotony with some funny quests, Guild Wars 2 manages to hide them behind a wall of illusion which works quite well for me. But not SWTOR.
I don't really like either of these 3 games. Guild Wars 2 is the closest MMORPG I've seen since Ultima Online to what I consider an interesting game, but still... I will keep searching.