I agree it's hard to write good abstractions, but the problem isn't really in Lisp per se - it's just that being able to express any abstraction you want cleanly makes you realize that coming up with correct abstractions is very hard mental work. You may refrain from doing it, but Lisp at least gives you the option.
Like, we all will admit that no natural language is inherently better than any other, but yet we still recommend that programmers learn English -- the quality of the language may not be inherent to the language, but it could be inherent to the context in which the language exists.
I don't think that's quite what PG meant by power. That being said, I do not think I would be able to close the distance between our understandings, sadly.
Or you could just say what you think PG meant, e.g. "by more powerful he means a language more easily manipulated and expressive".
How about that instead of the current comment ending that can be understood as "I've given up hope that you'll ever understand what I mean".