Disney are much, much bigger than you seem to think. They own Pixar, Lucasfilm and Marvel Studios. They already own a large chunk of the US cable TV market, including ABC and ESPN. They have just gained regulatory apprival to buy 21st Century Fox. They aren't newcomers to streaming, because they have a 30% stake in Hulu, which will increase to 60% after the Fox deal is completed. They also own BAMTech Media, which provides streaming video services for the MLB, the NHL, the PGA Tour and WWE.
Netflix should be very, very worried about Disney's streaming ambitions.
The sport is probably the most interesting out of all of those mentioned. There will always be a market for sports subscriptions, so they could have a very competitive offering there that Netflix aren't even involved in.
Marvel, Lucasfilm, etc. I'm still not seeing it. Two or three movies a year that I can pick up on DVD/Bluray cheaper. And that's if they're even worth buying on DVD after having watched them once in the cinema. Marvel movies have been wearing fairly thin, and Star Wars is showing similar fatigue.
I'm not saying they won't have a big market, Disney are huge afterall. I'm just saying that I really don't see them as strictly a direct Netflix killing competitor. They're in a slightly different game, content-wise, and Disney's biggest enemy will be itself.
Outside of your bubble, Infinity War is the highest-grossing film of all time. (With Black Panther following in 2nd or 3rd place if I'm not mistaken.)
Sure, Marvel does not particularly contribute to the pantheon of cinema, but it's nowhere near "wearing thin" commercially. Quite the contrary actually.
Netflix should be very, very worried about Disney's streaming ambitions.