Evolution of the AI.

No, in the fourth game and in Chronicles of Darkness, the bone dragon looks like a quite powerful fighter.

Well, that's your opinion. As for me, I just need to look at... well, even at his paws to understand that

Dragons are, by definition, reptiles.

in his case, it doesn't work; it's clearly a toad. His paws are in exactly the same position as a frog's. And in general, he looks kind of soft and slimy, although reptiles are always quite muscular and have absolutely dry skin.