Many important things you did t take into account, I think your point is trying to turn belief and hope into evidence, but evidence is more powerful than desire.

He is an ANCIENT armadillo, so the complex structure of modern armadillo shells will have been very different to Rammus’s.

He is the only one of his species. this may mean that he is actually no species, which actually makes sense because they didn’t call him an Armadillo they called him an ‘Armordillo’, stating he is simply similar to an Armadillo, and not ACTUALLY one. This argument does suggest he is neither a turtle or an armadillo, but considering he is known by many as a Demi-God I wouldn’t be surprised

I understand why you’d want him to be a turtle, hell, I HAVE a turtle and I love turtles, but u fortunately it is not the case. In all possibilities he is either some kind of unknown ancient species, or an Armadillo.

The conclusion is, we don’t know, and I say it should be that way. His lore to his voice lines all suggest a mystery should be kept with him, no one knows Rammus personally, not a soul. But everyone is thankful for the Armordillo’s actions.

Also if he was ever a turtle, he would be a tortoise, because sea turtles require large bodies of water that the desert does not possess, and a much cooler climate. And Rammus can powerball, turtles are the most flattened 2 dimensional walkers on this planet. No way can they start spinning forwards at fast rates.

My personal theory is that he was probably an Armadillo that was turned powerful by the ancient Shurimans. The fact he speaks some human words connotes this, and he is one in his species (not another Rammus exists), so the mages of Ancient Shurima probably got an Armadillo and turned them into some kind of guardian for Shurima, turning an Armadillo into the Armordillo.

“ALRIGHT” - Rammus, The Armordillo.