It would be if a WOTC employee came to my table every time I tried playing, personally overseeing every turn of the game to ensure that I didn't break the rules, engage in unsportsmanlike conduct, use my imagination, taunt my opponent or profit unfairly with their platform.
The above link is nowhere near close to exhaustive. Many of the formats on it were made up by fans, and then eventually made quasi "official" once a popularity threshold was reached, like Commander.
In fact, the entire premise, from the get-go of Magic: The Gathering was incredibly flexible modularity. Every time you change your deck, you're 'changing the rules' of the game. It's Turing complete, and people have made some really wacky stuff with MTG cards.
And, there's no small amount of proxying going on. Many, if not most Commander players allow a few proxy cards. High level tournament preparation involves 100% proxies. Online platforms allow you to play with any card in Magic's history for free, if you're willing to don the pirate hat; and if not, you can play MTGO or Arena.
And people did, e.g. https://en.wikipedia.org/wiki/Magic:_The_Gathering_Commander, which is now the most popular MtG format. So yes, even in this case the freedom to explore and experiment is good.
I love that example, since I have thousands of Magic The Gathering cards, but I have never played the game ever. The cards are very useful and I don't care what game they are meant for. Like many others I use Magic cards for print'n'play card games. Print out cards on regular paper, cut out, and put in sleeves with a cheap Magic card behind as backing.
Millions of people buy cards that can only be used to specifically only play, say; 'Magic: the Gathering' (MtG).
You could probably invent some sort of new game with MtG cards, or do some sort of card magic with them (no pun intended); but MtG cards are very intentionally not designed to be 'general purpose' cards or tools to design new card games with. They have a very specific audience in mind.
Magic the Gathering cards are also much more expensive than a regular deck of playing cards I can grab from my local dollar store. They have a lot less utility than said cards I can acquire for a $1.15CDN, taxes in; and they also have a bit of a stigma from people who seem to not like MtG for various reasons.
Somehow, still; it's one of the largest and most widely played card or tabletop games in the world; easily - and it's got an enthusiastic community of passionate and fascinating people.
Is Magic: the Gathering ruining card games? It is 'an offence against the entire notion of' what card games are?
Fuck no. Apple isn't some offence to the notion of computers, either.
Maybe it's not to your taste, but just because a product is designed for a specific set of purposes or utilities that don't suit your preference doesn't mean you have to jump to the dramatic conclusion that these products are 'ruining' the entire notion of what a product is. It's just a different product. Get over it, and use a different one. Take a valium and realize people like and use different things, and that's okay.
On a side note, I develop hobbyist apps for WatchOS, iOS, MacOS, the web; and SEGA Saturn, all on my Mac; and I've never had any issues actually achieving the results I wanted.