People have been talking about mechanical errata recently in regards to potentially changing rampage, and have been talking about the mass Errata that phyrexians got in regards to legends with that errata, so now seems like the perfect time to ask my question:You’ve said in the past that things like the mass errata to make things phyrexian is ok as functional errata because they were always phyrexian in flavor. That being the case, would legendary errata be acceptable for proper nouns from ABUR, Arabian Nights, and Antiquities, since they are from before “legendary” was even a thing? Aladdin, Ali from Cairo, King Suleiman, Bazaar of Baghdad, and Library of Alexandria are all proper nouns. 4 of those 5 reference people/places from the real world, which we know from the portal sets do constitute the “legendary” super type. You could argue that Bazaar and Library see to much play in extended formats to get such major functional errata, but the “phyrexian” errata to glistener elf and blighted agent turned infect from a fringe deck to basically unplayable in modern. I know you guys avoid mechanical errata if ever possible because it confuses new players, but I’d be willing to bet new players would be more confused hearing “Aladdin is not considered a proper noun. Nor is Baghdad” than they would be hearing “that card from 25+ years ago has been changed” especially considering many other old cards from around that time have had serious errata to their printed text that changes some of them SEVERELY. I guess my question is just: why is the mass errata of phyrexian acceptable, when it is changing things that were always phyrexians in flavor to be so mechanically, but an errata of proper nouns to be legendary from ABUR, Arabian nights, and antiquities not acceptable, when it would be changing things that were always proper nouns in flavor to be so mechanically?

Making a creature Phyrexian does impact how other cards interact with it, but it doesn’t change how the card functions in a vacuum. Adding legendary to a card does, and pretty severely in any 4-of format.

I think Infect stands out for its power level. Consider Double Strike, which also needs only "10 power" to win the game: there Double Strike at 1 CMC. The cheapest double-strikers with evasion have CMC 3 and 1 power. I assume Glistener Elf, Plague Stinger or Blighted Agent with Double Strike instead of Infect would be similarly abused.

Infect wasn’t powerful enough to be relevant in Standard. It’s playable in Modern because of access to a number of very powerful Giant Growth effects.