> It would make a lot of sense to go back to a smaller more integrated union with the countries which want it and leave the ones which only want the single market be part of a less integrated union.
That option does exist, albeit in a bit of a roundabout way. Nothing is stopping a member country from leaving the EU and joining EFTA and the EEA afterwards. The fact that no country is seriously contemplating this is telling.
That only going to a less integrated union. That doesn’t solve the issue of inner members wanting to go faster towards union and being hampered by countries which shouldn’t even be members like Hungary.
That option does exist, albeit in a bit of a roundabout way. Nothing is stopping a member country from leaving the EU and joining EFTA and the EEA afterwards. The fact that no country is seriously contemplating this is telling.