Why do i need to convince a core developer for my PEP? AFAIK the steering council can include non core developers (i know it isn't that current case but for the future this is important). And if the last authority who will approve my PEP is the steering council i just need to convince them not core developers.

Sponsors can stay (and they should because guidance is important) but thy shouldn't be mandatory. Let everyone to send their peps.