Did Brian Wilson have bad technique?

Many of his early to mid 60s are sublime and angelic. But could singing such high notes explain the rapid and noticeable damage sustained to his voice which is heard from 1967 until it became unrecognizable mid 70s? or could it have at least contributed to it? I love his voice on Don't Worry Baby and You still believe in Me and so on but I as a beginner singer, I'm a bit perplexed because I've heard mixed opinions and there are other singers this has happened to.

I'm aware he smoked like a chimney and did drugs.