I have zero interest (to the point of auto-conceding) to play against an off-format sized deck in a best of 3.

If WotC wishes us to take playing the format seriously, they need to enable a game mode that prohibits off-format decks. Those decks would not be allowed in FNM competitions and they shouldn't be allowed in MGT Arena competitions.

I'm all for allowing people to turn it off and enable a casual "jank-mode", but 90% of the time, I'm playing on-format. It's correct and respectful to expect others to do likewise and it is wrong-headed to match-make without taking this into consideration.