I just sent nebula an email outlining his complaints and my basic agreement with them. I've been a nebula subscriber for a long time and want to see them succeed - if Jeff's concerns are true (and I know the first one is - I thought they were working on comments when I signed up 5 years ago!), they're probably turning off more creators than just Jeff.
I think unlike YouTube or Floatplane, Nebula feels just fine being a closed system. Nebula is designed to be a single place where you go to view the content from the producers who run Nebula, not a single place for any content whatsoever.
They should absolutely try to make that set as big as possible though to increase incentives for paying for it.