I don't think Ernie's in much danger of being diminished, considering that he has a disproportionate amount of toys and merchandise compared to Bert and he has whole segments on Sesame Street that don't include Bert. The fact is that Bert is very underrated.
Of course the two of them together are what really counts, but lately, I haven't seen too much of that as it's mostly Ernie by himself. Besides, no matter how well a comedy team works together, people will naturally compare them to one another at times. I'm sure similar issues have come up with Laurel and Hardy, Abbott and Costello, Burn and Allen, Martin and Lewis, etc.
As a child, Bert was always that character that I related to the most and with whom I made up the most stories. One reason may have been was that I was interested in what it was like to be a "grown-up" and Bert seemed to fit that role better than any other muppet. One of the adventures that I created with my Bert puppet was that he had a secret life as "Super Bert" (Yes, a direct copy from "Super Grover"). I also made up a story about Bert joining the army and going to the moon. I was only about 5 or 6 at the time, but Bert seemed to really fuel my imagination.