maakbow I don't think that its necessary to lock the user to predefined classes (although I don't mind making things more fool-proof). Options provided by block editor are IMO already somewhat abundant and make it a lot easier for average user to "hurt" him/herself. However now you can document your theme and put inside some kind of manual for the user.
Either way, I hope adding IDs and classes comes soon to sections, because that would allow me to greatly both simplify and reduce the number of templates.