No one is paying money to see subpar hoops, the moment a player peaks he immediately goes to the NBA team. Minor League baseball is zero threat to MLB.
A strange comparison, IMO. Minor League baseball is an adjunct to MLB, a primary feeder system. They work in harmony, not in opposition.
The better comparison, IMO, is minor league baseball and college baseball, in which the former is by far more popular. And check out the Durham Bulls attendance figures versus ACC-baseball attendance figures.
Now professional baseball has been around since the 1870s and thus has a huge advantage over the NBA and NFL. They've developed a feeder system that none of the other American pro-sports leagues can match.
So, there's an apples-and-oranges component to this.
I don't like the word "cancer" relative to college hoops. If the NBA mandates two or even three years in college, along with high-school early entry, then lots of high-school players are going to be put in the position where they aren't ready for the NBA but are not inclined to go to college for several years.
So, the G-league and/or overseas are going to be increasingly attractive options. I don't think the NBA is ever going to go the route of pro baseball, where every major-league team has five or six affiliated farm teams. But the G-league is maturing structurally and increasingly provides an attractive alternative player-development system.
Colleges have the advantage of rivalries that go back decades, even more than a century in some cases and I do not think an expanded G-league is going to significantly erode that. A better G-league might marginally decrease the talent level at the top of the NCAA food chain but if it reduces the number of student-athletes with little or no interest in the student side of the equation, then that's a trade I would be willing to make.