If the account creation fee is not high enough to support 'normal' activity, then that is going to cause a problem.

I see what you mean, and I agree that keeps the solution simple for third-party developers. Maybe a good approach is recognizing a delegated Steem Power model is better for creating new accounts and under that model it's safer to introduce a multiplier to ensure the there's always plenty to go around (as it was before steemit made the change). If all onboarding systems took a similar approach, there would be less of a concern and it might end up being cheaper in the long run for those systems as they could just reclaim their SP for abandoned accounts.

raising the account creation fee.

If that makes the most sense to fix things quickly, I'd be ready to do it now (though I'm just a backup witness).

I also don't know the implications of changing the blocksize, but I do think it's something we should discuss with the experts before taking positions on.