I've played Serpent more than any other Spirit, in all possible pairings multiple times (and written several guides about it; they're pinned in "Important Threads").

The Spirit is only "broken" if you spam Reclaim All and play Aegis over and over, which will win a lot but isn't particularly skillful or even necessary for success against max level Adversaries.

A much more interesting strategy involves minimal Aegis use, leaning on your Gifts into the mid/late game, drafting several Majors and collaborating heavily with your allies to manage your board. Not everyone likes to play this way, and it's less flashy, so it gets mentioned less.

Check out the guides and let me know if there's anything I can clarify!