The problem of low level campaigns it was not the challenge or balance, It´s that low levels were plain boring.
In 2e-3.5 the first 5-6 levels you are basically autoatacking every enemy you see with your preferred weapon if you play a rogue or a warrior of any kind, because you do not have much more to do than that. Rogues, even if you can do some sneaky stuff you´re so bad at it that you usually fail a lot. Mages and sorcs have spells to choose but you could only cast them twice or thrice a day...
Newer TT games usually give the players much more things to do at lower levels and some class features that made the game more enjoyable from the start.
I beg to differ about lower levels being boring.
I'm currently playing a low-level campaign and only just reached level 3 last night when my halfling cleric killed a werewolf with an onion.