Bryan Fuller is still under an NDA. In the meantime all we have to go on are statements made by people who are friends with him and likely have some knowledge of the situation. Hence my use of "allegation" which could then inform how YouTubers are interpreting the current studio office politics.
We don't just have statements to go on, we have the fact that Fuller was fired from two separate shows for the exact same reasons and behaviour to go on. Also, what NDA? Fuller's been talking about Discovery for years including to people like Robert Meyer Burnett. Of course Fuller isn't going to say 'I got fired because I was irresponsible with the budget and made creative decisions which delayed production and incited further costs'