Personally, on bonus actions I go with what I think is the balance intent: you can’t use your action to cast a regular spell, and then cast a bonus action spell too. Regular action gets downgraded to cantrip-only in that case.
I disregard anything beyond that. So if you Action Surge there is no limit on your surged spell; there is no limit on reaction spells, etc. Because I don’t think those are what the ‘Action or (Bonus Action + Cantrip)’ rule was intended to address. Just a ridiculous consequence of the way it was phrased.