People will say Meet the Pyro ruined Pyro's character which is true but I think it really started with his voice. Apart from his maniacal laughs he doesn't really sound intimidating when mumbling other voice lines. I could see why Valve went with that direction. He was designed to be intimidating but the voice delivery not so much, iirc Dennis Bateman was just told to speak normally and mumble while covering his mouth to imitate the mask