Fair point with most of your post, though I think we need to define what is meant by the term "sola scriptura". It's a term not found in the bible, and I have both observed and experienced that arguing over man-made concepts leads to a lot of polarization and strife and is not helpful in the end. Different people can mean different things by a thing, or different details and nuances. Think it's much better to just look at what the bible says about God's word. Sure, He speaks to us in many various ways, but how do we test these things (as the bible says we need to do).....of course we need to test the spirits and test all things against the word of God, and what we learn in scripture about His ways and character as well. God's word is the plumbline against which we measure all things...and it is the only plumbline we have been given. Everything that man says and does needs to be measured against it.
What you are saying about "fundamentalism" is only sometimes true, as it is sometimes true about anything where human beings are involved. And what is fundamentalism anyway, that is another term not found in the bible. It can mean different things to different people...even those who call themselves fundamentalists have areas of disagreement. I would say fundamentalism is quite right in the fundamentals. "Ye must be born again" :)