Except that isn't the entire truth. I'd agree with you if all of the forms had the same stats and damage and the only unique thing about panther was its prowl, but that isn't the case. Panther also has the highest base damage (3d6) basic attack of any non-elemental myrmidon. But the reason panther sucks is its low dexterity. Other forms also surpass this damage thanks to strength elixirs, but it wouldn't really be a big issue if panther had reasonable dexterity.
Panther is really getting the short end of the stick in this game with nigh-infinite strength elixirs and the singular focus on tavern brawler. Which is why it could use some love.