First off Blitz is more-so a "pick" support than a tank, he's really not that tanky, but he can definitely carry a game purely on Good hooks making a teamfight a 5v4.
But yes, tank supports can carry, they just need a team that follows up, nautilus support for example is an old favorite of mine and good initiations and impactful ults and good peeling can absolutely win games.
the only people who think support can't carry either have a huge victim complex or are just bad at the role.
"b-but i can't carry when my whole team is bad" applies for every role.