Realistically, DRM is only cancerous to those who attempt to bypass it.
"Literal Spyware" It's literally checking to see if you paid for the game.
"Increased game size" Megabytes at most.
"Potential conflicts with game code" I agree with this, point well made.
"Internet connection" Had to be downloaded somehow, maybe activate on first use.
CD keys, would require a database that kept track of which keys have been used and how often, as we know, CD keys were just downloaded with the software, it's the least secure and is not a deterrent.
As @FadedOfTBTP mentioned, account integration would be ideal, perhaps if the itch.io app was to integrate this functionality.