I mean, the point of this card in any other format is going to be similar to something like Searing blaze, in that you are clearing out a blocker as well as doing some damage in one card. Burn as a deck really does not exist in vintage but if we think about how it operates in other formats we can come up with some heuristics to judge it by.
I think in burn you would only use this after you have maxed out on bolts, blazes, and maybe even chain lightnings. Games where you steal a Marit token are likely few and far between in any format. The list of creatures you can steal with this are pretty minimal, and many decks have some level of built in protections (ravager in shops to eat targets for instance).
Costing 1 goes a great length to make this seem playable, as does restricting MM, but this effect has simply just never been that important in the format to suddenly push this over the top, especially when you consider that the card is dead in some matchups not in a color that has to much relevant pitch cards for the format.