That's the worst description of Parachutes I've ever seen! There are only two of 11 songs with piano at all, and all the rest have Chris on rhythm acoustic guitar. It was very much the norm then, and not occasional at all. You're right about it being more stripped back and emotional of course.
Anyway, I agree with your argument in principle. As a guitar player, I've always viewed the arc in terms of Chris moving more towards the piano from the guitar and the sound moving more towards synths and layering whilst acoustic guitar is becoming more and more scarce. It really formed the backbone to the vast majority of Parachutes era stuff, and that's something that I kind of don't like. Each Colplay album that comes out is less "stummable to," you know?
I view AROBTTH and X&Y as classic albums though and am not at all disappointed, I just get that pang for the acoustic Coldplay beauty of old from time to time. I guess that's why Till Kingdom Come is one of my early favourites of the new one.