They just need to get an actual director this time, y'know? Stallone would do fine if he wants to do it. If he doesn't, I dunno, maybe Walter Hill or someone like that if you could convince someone of that caliber. Some 80s guy. Let them script it too, give them more control, Stallone collaborating with someone like Hill again woud probably turn out something decent - Bullet To The Head was okay for what it was.
Hell, McTiernan's probably going pretty ****ing cheap these days too, hit him up and see if he'd do it.
The two small-time guys that did each of the sequels is probably a big part (along with Lionsgate and a Lionsgate budget) of why they felt so weak & cruddy.
EDIT: The Chris, I don't know you'd want a Expendables flick with The Raid/John Wick type of action, though, it's sort of a whole other thing. The whole deal with these is they're sort of a love letter to all those 80s/90s (mostly western in style/feel/fights) action flicks. You want it looking and feeling like a classic Stallone or Arnold romp, nothing too glitzy & flashy. I love Wick, but that's straight-up Woo type stuff, a pretty different beast to what The Expendables is going for.