This is a really good write up, Max! Thanks for keeping up the effort while some of us are more worn out ^.^
I second most off your points as well, and you know the ones I disagree on already, more or less ^.^
For the record though:
13.7 We should not be able to cast 2 level 1+ spells during the same turn.
You're implying with this that you don't want people to be able to counterspell the enemy that is attempting to counterspell your fireball - something that you explicitly can do in core rules. Just like you can "Meteor Sarm -> Counterspell -> (action surge) Twin-Disintegrate", legally, in one turn... but you cannot "Shield of Faith -> Counterspell" at all. The bonus action spell rule is ridiculous and stupid in the RAW. Quicken spell, with Sorc, is the only actual reason it exists - and that should be controlled by rewriting Quicken itself. In Larian's game, the smoothest way to make the spellcasting fair and flexible is too leave us with the ability to cast with all parts of our turn economy, without an arbitrary limitation, and to simply rewrite Quicken itself to read:
"Quickened Spell:
When you cast a spell that has a casting time of 1 action, you can spend 2 sorcery points to change the casting time to 1 bonus action for this casting. If you cast a spell as a bonus action using this Metamagic, you can't use an action to cast another spell during the same turn, unless it is a cantrip."
This prevents the quicken spell break, but still allows player to flexibly cast with their Actions and BAs elsewise (as others have noted, there's no real 'break' with the actual Ba spells that exist) - and also allows them to counterspell mid-turn if they need to, regardless of the situation. So, this is the solution I'd like to push for on that score.
