I don't have much sympathy for Netflix since you can't acquire a standalone copy of most of their content (TV yes, but I believe to date they've yet to release an original movie on physical media) - you must subscribe to watch the videos. They sort of release in theaters, sometimes, whenever they feel like it, but the majority of their content is locked into their platform. I feel like Netflix would love for there to be zero requirements to show their movies in theaters.
On the other side though, Spielberg is well invested into Hollywood production, and it seems clear that he wants the Academy to shut out a huge competitor. For some reason, I don't take anything he's saying as genuine concern of film.
EDIT: I just thought about it. I feel like he's possibly trying to protect standard exclusivity agreements. Check out a related story when Netflix started a simultaneous release agreement with IPic: https://www.latimes.com/entertainment/envelope/cotown/la-et-...
The movie industry relies on theaters (and then royalties/physical media sales to a lesser extent) to make money on their content. The theater industry wants exclusive release windows. Netflix doesn't have either of these problems, and that's a threat to the standard business model of the movie industry. So I feel like that's why he's trying to push for a staggered release for Netflix, so that Netflix has to be encumbered by the same business model he deals with.