I'll grant that Chuck is correct that Strayhorn influenced change in Ellington, I just think that change was good. As Tony mentioned before, Ellington was writing songs before, and Ellington had a real and serious need to have singers for songs in his band and Billy's arrangements for these were top-notch and a boon to the Orchestra which had to compete with the other bands for attention for vocalists.
I also think that a lot of Strayhorn's work is largely unnoticed as his, and the contrast that he provided to Duke's music within arrangements made for strong and interesting pieces. And the individual compositions he presented are wonderful.
To my way of thinking there's a chance without Swee'pea the Orchestra may never have made it into the fifties in the manner that it did, and we would not have the rich body of work we do have to study and enjoy today.
Hey, I'm no fan of the AEC, and if they had had a Strayhorn-like organizational influence and more form for me to perceive I would like their work more. Yet Chuck loves these guys to pieces. So there's different approaches and different tastes. I've been wearing mine for a while, I like them, I know Chuck feels the same way.