No time to reread all of the posts/analysis. I'm just going add my current numbers. The wizard transmutes do a pretty insane amount of damage.
Assumptions
I used Elf Wizard (which I normally play, for my analysis)
Only spells that currently have a skill test listed will get the enhanced skill test. That is Magic Missile, Acid Splash and Shocking Grasp. It may have been alluded to previously, but I haven't seen it stated in the latest iteration that the new scroll/spells would also gain a skill test.
I assumed 3 combat rooms and a total of 8 rounds (very typical for a nightmare group). These numbers really do not apply to normal or hardcore runs. If you have all of these tokens, you shouldn't be running at those levels. If combat goes beyond the 8 rounds, the wizard ability diminishes quickly.
I'm assuming in 2021 that I can use my 2nd and 3rd level spell free actions from the new legendary and swap out the 3rd and 2nd level spells for more Magic Missiles
Build (items that contribute to spell damage, unless listed the bonus is the same for both years)
IS Banshee Prism - +2
Eldritch set - +3 in 2020/+4 in 2021
Bracelets of Cabal - +1
Arcane Belt - +2
Boots of 4 Winds - +5
Drake's Staff - +5
Relsa's Ring - +5
Shirt of Focus - +2
Earcuff of Inspiration - +4 (assume legendary level bard)
Lenses of Focus - +1
Gregor's Tome - +2
Total bonus damage - 32 in 2020/33 in 2021 (due to added eldritch item)
2020
Room 1 Round 1 - Fireball using MEC plus Magic Missile using Cabal = 115 damage
Room 1 Round 2 - Magic Missile using MEC = 54
Room 2 Round 3 - Fireball from COE using MEC plus Magic Missile using Cabal = 115
Room 2 Round 4 - Magic Missile using MEC = 54
Room 2 Round 5 - Acid Ray using MEC less 10% miss chance = 52
Room 3 Round 6 - Fireball from RoSS using MEC plus Magic Missile = 115
Room 3 Round 7 - Ray of Shock using MEC less 10% miss plus Acid Splash using Cabal = 99
Room 3 Round 8 - Ray of Shock using MEC less 10% = 61
Total Damage = 665 points
Extra Ray of Shock and Magic Missiles acquired through Charm of Spell Swapping
2021
Room 1 Round 1 - Magic Missile using MEC plus Magic Missile using cabal = 135
Room 1 Round 2 - Magic Missile using MEC plus Acid Splash using Medallion Free Action = 130
Room 2 Round 3 - Magic Missile using MEC plus Magic Missile using cabal = 135
Room 2 Round 4 - Magic Missile using MEC plus Acid Splash using Medallion Free Action = 130
Room 2 Round 5 - Magic Missile using MEC plus Magic Missile using RoSS = 135
Room 3 Round 6 - Magic Missile using MEC plus Magic Missile using cabal = 135
Room 3 Round 7 - Magic Missile using MEC plus Magic Missile using Medallion Free Action = 135
Room 3 Round 8 - Magic Missile using MEC plus Magic Missile using Medallion Free Action = 135
Total Damage = 1070 points
Extra Magic Missiles acquired through Charm of Spell Swapping, Ring of Spell Storing, Charm of Power and Crown of Expertise
Basically the skill test bonus pushes me to use magic missile as often as possible to the exclusion of all other spells. Unless the scrolls gain a skill test, they are worthless unless needed situationally. Similarly, you may want to use a fireball or two in rooms with more than 1 monster.
So the net gain over 8 rounds is 405 points of damage. Most of this is a result of the FA spells. A good chunk does come from enhanced MEC.
What do you lose?
In 2020 I had 64 hp, in 2021 I have 52. This assumes I add the new transmute IS.
I am unable to equip CoAS, so the entire party loses 1 hp and the party loses 1 to initiative rolls.
My saving throws go from 19/22/18 to 14/17/13. So there is a greater chance that monster effects will either damage me or stop me from casting my spells altogether.
Token losses that sting - Charm Necklace, Charm of Awakened Synergy, Charm of Brooching, IS Charming Cabochon, IS Topaz Trilliant, Cloak of Shadowskin (Or Greater Destiny), Semi-Lich Skull
I could look at dumping the Cabal set, but would lose 168 pts of overall damage. I could get some stuff back by losing the Arcane Belt, that would cost 32 points of damage, but I get 1 Charm and 2 IS back.
Anyway, every round past round 8 would be an Acid Splash or Shocking Grasp using MEC for 69 pts of damage. You would still have a handful of spells left. Not enough for grind, but plenty for the dungeon.
I'd love to cast more damage, but this is kind of excessive. Also, it's kind of boring to just keep swapping things out so I can do two magic missiles every round.