I'm not sure I believe this to be true. There's a lot of powerlevelers out there, always has been. In initial days it more resembled the masses parked at PI begging to join Fire Tank teams, then it shifted toward hazard zones and farming, and later into AE. There was never a shortage of it, there were always consistent complaints about the PI begging and AE usage, enough to influence the devs toward changing that. And there were a lot of guides, from where to best farm, the different ways of farming (who remembers box farming), strategies for tanks to keep aggro (BLOS yo!), and best builds geared toward farming. Heck, I may have done a guide back then on hazard zones and leveling.
So I think it's our relative experience with the game and the people we played with that probably informs your opinion on this. And it's true for me as well, we are both speaking purely anecdotally. But I still believe it's utterly true that there was never a time that powerleveling wasn't a significant portion of the game, and people's distaste of it frequenting the forums.
I don't know of any current guides, as per the OP. But hit me up if you have questions, we still use hazard zones a fair bit for alts and I can suggest such for your level.
** Or I could list them here. General flow is Atlas or sewers until 5-6, then Perez Park or Hollows from 6-10/11 (Perez outside of walls is best), then Boomtown from 10/11 to 20/21 (Faultine is possible but worse), and Striga Isle for the 21-30 range. It works best if you have AOE oriented characters, and runs much smoother with a group than solo, although solo the xp is flat out better. Use inspirations as needed (heavy on purps/blues), and focus on the bigger groups of enemies, wiping out a group them moving on. If you run into endurance issues every fight, I suggest finding groups at -1 level until you get your endurance settled. You can do the same via missions by setting your notoriety team size larger, but I don't think it's as efficient as hazard zone leveling. We commonly run Dom/Troller/Blaster, or Troller/Brute/Corr trios, but the more folks you get the higher level you can fight so the xp flows. Enjoy.