Turning it into a panda can be even worse: now you’ve made it harder to kill, better to buff, and used songhai’s only “hard” removal to give the enemy that advantage. Sure, you can phoenix fire it, or twin strike it, or crescent spear+damage spell it, but the point is that you will spend a minimum of 2 or more cards (roughly 5 mana or more) to remove a turn 1 terradon as songhai by about turn 2 or 3 depending on your mana spring efficiency (again, unless you have it’s specific counter, spiral counter…which won’t work if the terradon has been buffed or hasn’t attacked).
I don’t think it’s OP, but it’s efficiency makes it darn close, especially if summoned out the gate. 1 increase to it’s cost would balance it with the more low cost golems instead of much better. I know there are ways to remove it, and there are stronger cards out there, but it’s efficiency is what makes it a threat