I really like the idea of mercenaries but they can be improved upon.
First biggest issue I have with mercenaries is that their damage doesn’t scale at all. they do quadruple digit damage only when players are hitting for billions. Mercenaries should scale with players stats/level/paragon/ and damage. Mercenaries should inherit all the player stats. I don’t think mercenaries should equip gear in D4 because gear is too class specific while mercenaries are like their own classes all together. For this reason i understand why mercenaries don’t equip gear and personally I don’t see how a gearing system would work for them. There should also be a deterministic way to scale mercenary damage. We should have uniques and aspects and tempering manuals for this as well.
Second thing is that we need to be able to customize the appearance and skin of the mercenaries. This is a wasted opportunity for Blizzard. Also let us change the mount skin that the mercenaries ride with any mount transmogs in our stables. This would be very cool.
Third is that I think the skill trees should for the mercenaries should be bigger, but Blizzard likely won’t do anything about it until the next expansion. Also we should have more mercenaries. $ is not enough. Blizzard should add more. How about like the scholar who does lightning and frost damage? Or a mercenary that does poison damage.