Merc Speed Leveling Broken?

Mercs appear to be account bound, meaning you can have a high level Merc accompany you while doing the campaign. Is this too OP, or is it GGG listening to players who want options to speed up repeat run throughs on alts?

You have to be withen 20 levels of your merc

There is supposed to be a 20 level difference maximum. Is it not working for you ?

(And yes, quite powerful indeed : add to this the 70% relaxed item level requirements, and the usual 80% one on affixes...)

But then too low level mercs suposedly won't spawn, and you have a limit of 3, so you would need to use these precious slots or keep mid-level merc recruiter character(s)...

Well that is a net good for the game, even if I was planning on steam rolling through content. 20 levels is still a lot. You can just use a Merc 10-20 levels higher and rotate out. It's a bit more complicated, but significantly faster, especially when Scion's suck for leveling.