It seems like Gruenwald really underestimated how hard Roger Stern would be to replace. The Avengers in the '80s were not blockbuster popular, but Stern kept them solid despite not having access to many star characters.
And when you remember what a bad place the Avengers were in when Stern took over - they'd gone through issue # 200, then a year of mostly filler stories, and then Shooter's infamous second run - it's even more impressive how Stern managed to right the ship.
Of course, to bring this back to saying good things about Gruenwald, that's also a tribute to his editing, since he started editing Avengers just a few months before Stern started writing it, and he managed to turn the book around and even make it strong enough to get a spinoff.