I reiterate that it's yet another unfortunate side effect of 1990's kids programming. Elmo jumped into the spotlight at first out of necessity... Jim and Richard's characters were gone... Frank's characters weren't around as frequently... and after a while the whole reinventing of Sesame Street with the Around the corner stuff faded from the show. Characters started to gravitate in favor of the Crowd of Elmo, Zoe, Telly, Rosita, and Baby Bear (the last, mainly came out of David Rudman needing a regular character... this clearly before he took over Cookie Monster's role). But Big Bird, Snuffy, and Oscar were still frequently featured.i have to say this that , i like elmo and yes though at times he does still the spot light and that does get a bit over bearing but he is a cute little guy and he is a big part of SS .
Then came Elmo's world, and TME, and we know what happened next. I really blame the whole Barney aesthetic for it, as I said above... instead of having a group of fun characters to play with, we have one central character with a couple assistants, and it's a whole matter of self centered-ness... all from Barney.
In the 1970's, Early 80's (and even a little after that) there was a LOT of focus on Grover (mostly books, I want to say)... but he shared the spotlight. Something tells me Elmo could have if they kept the show the same as it always had been.