Quote from DirkGently »
Birgi is currently among the least-played commanders from the set and I doubt that'll change. Compared to Kykar she's waaaaay weaker. Saying she's stronger because she works with creatures is pretty ridiculous imo - creatures rarely lend themselves well to storm (maybe in green if you count elves, but not in red afaik). The only creatures I'm aware of seeing much play in modern storm lists, despite not needing to build around Kykar's ability, are ones like Baral and Goblin Electromancer that reduce costs for the instants and sorceries that are doing the real work - and those creatures are (afaik) all blue. That's not to say she won't see play in cEDH, she likely will...in the 99 of existing storm lists with more powerful 2+ color commanders which let you run crucial blue enablers.
Comparing birgi to kykar is a little awkward. There are different routes and styles of building a storm decks, and having one that can work with creature casting is good news.
Adding colors (specifically blue) almost always yields a spell slinger style, but creature based storm strategies already exist. Past the obvious empty the warrens+purphoros, once people see what older cards like grinning ignus, leering emblem, scroll of masters, storm entity, and haze of rage can do with Birgi I'm hopeful that it will open up ideas for future cards.
She very well can work as a commander. With the sheer amount of filtering in wild guess variants and reds recursion with mizzix's mastery/past in flames/recoup/shred sanity/etc, it's a very simple shell to build and will only get better as new cards come out.
Is it high powered? Not currently. But it's a new option that wasn't there before.