He had final say over use of muppets. Elmo only skyrocketed in screen time after henson died
Not really. Maybe in the early years, he did, but it was pretty much left to the writers (and whichever puppeteers were available for filming) which Muppets were used. You forget that Elmo did exist when Henson was alive and did plenty of bits with him in that brief period. Now there's no knowing how Henson felt of the character at the time, but I don't think he would have had much say into how much he could be used. Although, I will say, if Henson and Oz had spent a little more time on set in the later years, we probably wouldn't be talking about Elmo right now.