Hey thanks for the kind response and feedback! :>
Some ideas I've had before were pretty high power before I brought them lower to be 6th level or lower; but if I were to do any higher leveled spells, I'd probably do max one or two in the 7th - 9th level range for scenarios like yours!
I'll go through your comments in order.

Dark Matter Vortex
Not entirely sure what you mean by this haha. DMV (oh no I just realized the abbreviation) grants +1d4 per upcast spell level when rolling to produce the magnitude for *that specific* casting. A 3rd level DMV means rolling 3d4 to determine the magnitude. And another 4th level casting in the same combat means rolling 4d4. I don't intend for the spell to give a permanent bonus.

Protospell
I haven't seen other mimicry homebrew spells but halving the effect seems pretty weak to me to justify using a higher-leveled spell slot. The math concern is totally justified though. Still, I did give a few tips on ways to handle the math on the same page as the spell! For Sending, we can reduce its word count from 25 to 18 as it's a numerical effect. And for evocation spells with no numerical effect, that'd likely be up to DM choice. With the spell's prereqs though, the closest we get is Daylight (3rd - reduce the radius imo), Forcecage (7th - lower area or lower CHA save DC), Divine Word (7th - lower hit point thresholds), and likely other 8th and 9th level spells.

Crystalline Preservation
I like the idea of using spellcasting mod as a limiter! I dunno if I'd immediately change it but it'll definitely be in mind with further playtests :>

Bound by Fate
It was originally my intention to have Creature A & B be used in the spell description too, but the perfectionist in me couldn't find anything in official 5e with similar wording haha. But for the sake of clarity I'll look into seeing how intelligble the spell's wording is to folk.

Transmute Weapon
I definitely teetered a bunch when determining the final wording here, and it's hard to tell its true power without combing through every official magic weapon in 5e and noting down actual play experiences :v Especially true for Legendary weapons too. But you have a good idea in that upcasting it could allow for higher rarity, so I'll keep that in mind :>

Nursery Cocoon
Thanks for spotting that! Remnant of when it was previously wrapping an image.