The best NFL analogy is the AFC East. Through a superlative QB who took a lesser contract to remain, a fantastic HC, and very astute roster management the New England Patriots remained on top of the AFC East for two decades. And went to the Super Bowl nearly half of that time period. Now it didn't have an overall effect on the NFL, but I'd argue that it had a definite effect on the other teams in the AFC East. Buffalo, Miami, and New York went through a host of head coaches and GMs, each trying something, anything to catch back up to New England. And each quick trigger move set each team back, to the point where the Jets, Bills, and Dolphins were basically averaging about 4 wins a year each. The Patriots won seventeen out of nineteen AFC East titles, and eleven consecutive. By the late 2010s, each of the fan bases of the other three franchises were likely diminished. What hope is there as a fan of the Bills, Jets, or Dolphins if you know that you cannot compete.
The Crimson Tide has had a similar effect on the SEC. They're so far ahead of the other teams that it's diminishing hope that anyone can ever beat them again. And when extrapolated to all of college football, where the same three or four teams are in the four team playoff every year I can almost guarantee you that within ten to fifteen years time college football will be a niche sports, consisting of two or three dozens teams and enjoyed primarily in Alabama, South Carolina, Texas, and Ohio.