Mouseferatu
Hero
I address this sort of thing in my game's table rules: "'Metagaming,' defined as using player skill or knowledge that a character might not necessarily have, is fine as long as it's fun for everyone..."
And this is where it breaks down.
I mean, not for your table. It clearly works for you, and that's good. But in more general terms.
The whole idea of the the fighter-frog happening to leap onto his friends' blades because the player knows that suicide ends polymorph? That's the sort of metagaming that is absolutely not fun for me, as either a player or DM. In fact, it can straight-up ruin an entire scene, if not an entire gaming session.
Unless we're playing a 100% slapstick comedy, it shatters all sense of fictional cohesion for me. I would sooner change the rules of the spell, even if that made it clearly mechanically broken, than want to participate in a game that included this sort of "solution."
(And no, we don't run "serious business" games, either. We spend far more time laughing than doing deep-immersion RP, even if I'd love to see more of the latter. But there are limits.)