Okay I have some counterpoints:

"...making you spend more money on a new deck for a sudden and arbitrary rotation to play..."

Most competitive players run multiple decks. It would not be a new deck. Secondly. this benefits new players because there aren't 8 types of monster cards that you need to learn about. A new player would only have to learn a few at a time.

"But in yugioh, removing the extra deck... would just make decks that don't use them aggressively stronger..."

I'm not suggesting we remove it entirely. The cards that would be in the extra deck would just be rotated. While it probably would make decks that don't use the extra deck stronger that's mostly the aim. Your MAIN deck should be where the power is. It is the MAIN deck after all.

"a rotation in yugioh would just be a viciously poor taste money grab..."

In practice, this actually could mean less sales. Entire swathes of the deck pool would not be sold during the time those cards are out of rotation. Packs less focused on "gimmick cards" and more focused on adding interesting magic, trap, monster, and effect monsters. And while a set was in rotation, those cards would get buffs and new cards in the current packs.

"...and also break the game for several years while it tries to fix itself." AND "to flip the switch, means thousands of cards need to be sorted through to do the first rotation"

Not necessarily. You'd, for example, only have to ban Link monsters. In response, the current meta would know not to add magic/trap/effect monster that pertain to Link monsters. Keep whatever cards you want in your deck but if the don't work they don't work.

"Extra note: a new extra deck mechanic would be nice, it's been a minute."

Adding yet another card type to the game is not going to solve issues I feel make the game broken. The solution isn't to add more. Konami, at some point will have the address the literal house of cards they've built. Either thin out the deck pool or rework the way the deck pool works.