2) The surfaces are a cool addition in my opinion, but maybe a bit too much of it.
3) The player ranger can't summon a companion in the middle of combat, as far as I am aware. You can summon a familiar or if summon while sneaking out of combat to begin one, which I don't see how to prevent. In general, I like what they are doing with the ranger in BG3 because official 5e content Ranger abilities are useless in combat and irrelevant in high tier play. Note, I love the Ranger archetype, and play it, but sometimes I just wish I rolled a Scout Rogue.
4) I think giving enemies a better arsenal is exactly what this game needs, because it is much more focused on combat. It would be boring to fight standard goblins all the time, at least in my opinion.
Agree on 1 and 5
I wouldn't mind giving enemies more tools if the number of enemies got reduced to compensate. 5e combat is largely decided by number of combatants and both sides and how many times they can act or attack in a given turn. The GENERAL rule is if both sides are around the same CR the side with more actions will usually win statistically.
You can try this yourself in the Goblin Camp actually! If you aggro the initial gate guards and save/heal up before engaging the fortress you can play out the scenario literally and theoretically a few times. When the rolls are good and you have a plan of action you can steamroll the entire area.
When they aren't however, if you eat a crit, whiff attacks that would otherwise remove the combatants constantly and the momentum swings in the enemy's favor you will slowly get snowballed without the crutches of all of the items. Even purely by numbers, if you reduce the game to the basest stats each of the NPCs have and remove the busy work of surfaces, bombs, consumables/ect? It gets a LOT more manageable on pen and paper.
I'd love to see this stuff in Divinity Original Sin 3, NOT Baldur's Gate. They need to return to form or trust that the PHB/Monster Manual CAN be fun if it follows the formula first THEN is tweaked afterwards.