Agreed, there will be a market, maybe even a large one but I don't see it out growing on the field / on court sports. It will be interesting to see how it evolves, if they go the route of European league soccer organizations it may work out for them because one major issue is fragmentation. Simply put, there are too many games vying for viewers, new games coming out all the time, and new expansions or iterations of existing games coming out too. The fragmentation will forever be a challenge IMO and leads into another major hurdle they have yet to solve which is longevity of a particular video game.
Yes, the games of Basketball and Football, etc. change over time but they are by and large the same. Competitive StarCraft was once the case example for esports and has mostly died out. StarCraft II was a bit of a flop from a competitive standpoint. Are kids 10 years from now going to care about Counterstrike? Or PUBG? No, they'll want to watch people playing whatever new games have come out then. And that's a problem for retaining talent on these esports teams as well; the greatest and the skilled of the elite players in one game don't always translate from one to another. Yes a great COD player can transition to Overwatch or some other first person shooters, but Minecraft? Rocket League?
ESports are kind of the wild west right now along with a lot of other things in video games in general like loot boxes, lots of money to possibly made but lots of challenges to iron out. Their regulating bodies are either non-existent or extremely weak. For example, illegal PED use is extremely rampant among eSports players. This is well beyond the old days of gamers chugging Mountain Dew and such for a caffeine fix, most of those kids playing competitively are taking Ritalin, Adderall and lots of other drugs. This is to say nothing of the gambling issues, truth in advertising, and competitive shenanigans (collusion, cheating, hacks, etc.) that are pretty rampant out there.