As for the last scenario, I can categorically tell you that whilst technically not breaking any rules of the game, that is not how fights happen. I practice HEMA with friends and if you tried to force your way between 2 of us standing a few feet apart you would be in a whole world of pain. Of course if you run everything in exact multiple of 5 feet then maybe there would be space
Yup. Again, if you adjudicate with some set of real world aesthetics that the rules do not actually have, then yes, a lot more "players talk the DM into gaining an edge" things are possible in the game.
I will point out that we use hexes in our game, so some of the stuff that you talk about just do not work for our table.
Plus, there are always examples where "Woo Hoo, the wizard did great.". In 20 encounters and about 60 to 70 rounds, I've seen it happen about 5 times. Maybe.
I'm starting to thing that the main way to shine with a low level 5E wizard is with the Sleep spell or with Illusions. Everything else is just so situational and subpar. Even good sounding spells like Grease are SO situational, In a small area, yeah, Grease can help. In a large area? Really situational.
My wife has a Bard and took Silence as her second level spell. She took Silence for one reason and one reason only. To slow up enemy spell casters. That's it. She faced off against an enemy Cleric and could not even cast the spell. The cleric was some distance back in a larger room (about 60x80) and all the cleric would have had to do each round was move out of the area of effect. My wife would have had to cast the spell 3 times to guarantee a result.
The main purpose of the spell historically in D&D, totally defeated by the 5E rules. And yes, if the DM rolls for a random direction for the Cleric to move (and ignores the fact that the DM knows where the spell effect is) and my wife would have known to not center the spell on the Cleric, it could have prevented the Cleric from casting for a single round. But still, that's a stretch. The spell is farily situational. It only works real well if the enemy cannot move 25 feet and get out of it (like in a smaller room with no exits on the other side). Unfortunately for my wife, that was not the case that day. She had gone out of her way to handle this one situation and the one time it happens, the spell is for all intents and purposes useless because WotC nerfed 5E spells.
Edit note: Silence is a concentration spell that cannot move, so it is impossible for a single caster to cast it 3 times. Not only has it been nerfed to not be cast on a foe with a save, and nerfed to no longer be movable, and nerfed to be broken with a concentration check, but also nerfed with regard to how often it can be cast. Once. It is now almost totally limited to small areas where the foe does not have an exit. If you can lock down a foe in a small area and prevent the PC casting Silence from getting damaged, Silence can work. Most of the time, it's more or less useless.
Silence is listed on the WotC Bard optimization page as light blue. It's nothing of the sort. It's so situational. If the party can lock down an enemy caster, then it can work. But there are so few ways to do that anymore. Most of the lockdowns have been nerfed. An enemy can sometimes disrupt a grappling Bard using it with a single weapon attack (and of course, a grappling Bard needs 2 actions to get this combo even started).