I'm neither in SV nor a webdev. I just remember how many ordinary users hated the ribbon when it first came out. Presumably they adapted over time; I can't really speak to whether Microsoft would have been better evolving the existing menu system. Personally, I could take it or leave it--and at least intellectually the arguments for the ribbon made sense to me.
Ordinary users hate change. They always do, regardless of how successful (or not) the changes are later judged to be.
This doesn't argue against change so much as argue that the costs need to be worth the disruption - you don't move houses over a carpet stain, and you don't rebuild your UI lightly, either.
Office is a professional productivity tool that's been around for decades and is used by millions of people for their entire workday, every day.
Learning to use a new tool takes a tiny fraction of the time you're going to be using that tool. One should make the tool best at actually doing what it's going to be used to do.