Unlike Stritch, Morse had a better Broadway track record, having starred in one smash, "How to Succeed.." and also had starred in "Sugar" which ran about a year, and had appeared in films including of his famous stage hit. Plus he made a great return and won a Tony for his Truman Capote on Broadway in "Tru" in 1989, just about 5 years before the "Show Boat" in question. While famous for "Company", Stritch played a supporting role in its success. Stritch starred in some other shows in NY like "Goldilocks" (and as one of my favorite flops, she sounds wonderful on the OCR), but her track record still wasn't as good as Morse's, which is why at the time of "Show Boat", he seemed to be the bigger star. Morse had a few flops like "So Long, 174th Street" and had also been knocked down a peg perhaps by getting under the title billing when co-starring in the tour of "Sugar Babies" with Carol Channing alone above the title. It is a bit surprising that there didn't seem to be enough comedic/character leading men type roles for Morse during that time. Both Morse and Stritch had personal health issues, too, which may have affected their careers for significant periods of time.