Hair-splitting is what ... well, if not quite all of it, to bifurcate yet another follicle ... much philosophy is about. Not necessarily of the proverbial angels-on-the-head-of-a-pin variety, but damned close.
It's where the, erm, quality is.
(You'll know it when you see it.)
I've had my own issues with ZAMM, having more to do with some of the thinking striking me as excessively fuzzy. I suspect much of the appeal isn't so much as an authority as a bridge -- connecting people with backgrounds in the mechanical (motocycles), and possibly in computers (Pirsig's own field, other than philosophy), to philosophy proper.
And it's got some good bits and observations.
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Notes:
1. In particular, Peter Adamson's excellent "History of Philsophy Without Any Gaps": https://historyofphilosophy.net
Though also other (and direct) sources.