My opinion is that Red Nichols lost control of the artistic ship when, beguiled by Teagarden, Goodman, Krupa et al, he scuttled Miff Mole, Vic Berton and the whole collective improv idea.
SURE Red made some excellent records after 1929. But they increasingly represent someone else's vision. Where he once had an ensemble that evolved organically, and sounds just as unique and original as Duke Ellington's, he gets gradually more conventional until by 1932, you can't tell his band from anyone else's.
And this goes for his solo style, too. His 1925-29 solos, comparisons with Bix aside, are decidedly original. There's NO mistaking him for any other cornet player. After that, he flounders artistically. Not technically, but creatively.
I do not entirely blame Red for this. The musical ecosystem changed drastically. The Great Depression seemed like the end of the world. SO many people lost their way and even their lives because of it.