The NFL has taken a 2 year hit in ratings, no doubt. The NBA, OTOH, has seen more upward growth up until this latest season. Cuban is right, right? (post hoc ergo propter hoc).
The NFL's TV numbers being so utterly dominant that growth would be much more difficult than the NBA's very solid but FAR from NFL ubiquity numbers. The NBA could see growth for years while the NFL see fall backs for years -- yet the NFL will still be bigger in terms of per event nielsens. The NBA numbers are good and need not apologize to anyone, however, the NFL even now remains absurd in its numbers.
IMHO once the NFL embarked on the PR justice of Goodell the stage had been set for softening numbers. The outcome of PR justice is always going to be having show dishonesty, talking out the side of the mouth, unequal actions and eventually alienation of potential viewers with ever greater group/demo diversity.
On CTE, yes it is a serious issue but I don't believe CTE has tangibly hurt the NFL numbers. IMHO this is akin to boxing in its greatest days. Fans knew, deep down anyways, a guy getting his melon bashed for 20 minutes that somehow staggers to stay on his feet so he could get his melon bashed for an extra 5 minutes ain't gonna really gonna be good for that guy's health. So even if CTE wasn't yet defined and known, were there that many who actually thought the bashing of skulls (even with helmets on) over a 10 year career was ok for that guy until CTE was defined?
Consider this: years ago people would line up to see Evel Knievel jump a motorcycle over a country mile of buses. Sure, hey, sometimes Evel ended up landing a bur or two short which caused him to do a 180 MPH cartwheel down 10 city blocks. Ahem, that was just part of the sporting event, right? There are 1000 other different ways a human has presented themselves (in sport or individual action) where danger and threat of violence/doom has packed in the crowds. This is part of who we humans are going all the way back to the Roman Coliseum and before. So IMHO Cuban is making that simple minded A-B connection that has a much deeper, logical explanation (some of which isn't PC to speak about -- that humans like to watch danger/threat of violence, admire those who will willingly face it, and we will never really stop to consider the 10 year or 20 year later ramifications even though most are smart enough to know the ramifications have always been very possible).