Yes, PG is influential primarily because of his writing. He wrote
On Lisp, which is still well-regarded today, before founding Viaweb. Viaweb itself did not make him well-known; there were many newly wealthy dot-com millionaires at the time, and he was just one of many, except that he wrote far more persuasive essays. At the time that I wrote
https://paulgraham.com/redund.html we were discussing programming language design on a mailing list, and there was not yet any suggestion of a VC fund.
The reason he got into venture capital was that some of those essays urged ambitious young people to start startups, drawing on his own experience, and specifically to write SaaS software in Lisp, as he had. The Y Combinator fund came afterwards, and its dealflow came from the people who had been persuaded by those essays. That's why the first version of Reddit was written in Lisp.
If Y Combinator had not been successful, he would have remained well known for his essays.
Though some of his ideas were not correct, looking back, it is hard to name any other writer of persuasive essays of the past quarter century whose work has been similarly impactful, except perhaps Mencius Moldbug. Moldbug's work may turn out to be less impactful—I certainly hope it does—but it's too early to tell.