It has more to do with revenue sharing than competition from any start-up leagues. The revenue generated from TV. Without it, small market teams would not be able to compete financially. Eventually, the league would eat itself.
So what you’re saying is that this all has to do with Team CATV arrangments & the launching of the NFL channel? Lovely.
Which strikes me as ridiculous. Teams compete on the field but are franchisees of the same company. The Yankees can't entertain their fans and make gobs of revenue without a visiting team. I'd bet if you looked into it it, the whole anti-trust exemption thing sprung from some sort of labor relations thing. Democrats seeking to enlarge the base to include athletes.