Clark Burroughs did some/a lot of vocal arrangements for/with The Association.
So sure, both him and Puerling were aware of the younger groups. But Puerling was aware of a LOT of musical things that they were not. Musical knowledges that had nothing to do with cultural trends or other extra-musical considerations.
There is no substitute for skills, no substitute for knowledge, no substitute for knowing. The more you know, the more you can do.
Or not do. But knowing gives you the freedom to choose.