Perhaps, but I just note two things: last year, about 11 brand new teams were assigned to my D5 league, and this season only two at the very beginning. That is coupled with last year a fairly large number of bots in D4 that would support bot cleanup promotion from D5. This year there are few bots in D4, and likely there will be few teams promoted via cleanup.
And actually I think it's bad for new managers to get put straight into a D4 league. You're not ready to compete, and I think it's likely that some managers would become frustrated with the game quickly. Better to leave open teams as bots and fill them with the best non league champions from D5.