This post warms my heart - really, good to read it drives others mad, too.
Two in-depth articles from a longtime Max user about PBR and some of its assumptions and pitfalls, and practical solutions:
https://www.racoon-artworks.de/blog_PBRfromrulestomeasurements.phphttps://www.racoon-artworks.de/blog_PBRshootingandcalibrating.phpGetting the right material properties is hard without a proper device. A colorimeter will only give you a reflected color value without any other info about reflectance and its behavior. The there's the materials surface which will affect all incoming/outgoing light and will produce different results for lighting and viewing angles.
Then there's the renderer - you can't really be sure how realistic it'll model the reflectance behavior when it comes to surface structure, how bump maps work in renderers is generally very simplified and will not reproduce real life accurately, and with texture filtering you can not really tell what it'll do). Rough diffuse materials are really a topic on its own with hardly any renderer caring about it.
As for sRGB, it's only getting worse from here. I'd say the range of colors in RAL and Pantone that can't be reproduced in sRGB may even be about 50%, maybe even more. I have not once come across a site that will tell you which space of RGB they assume for the values, and I'm pretty sure it's because they know it's impossible and just tell you a number close enough. Some vendors will give you LAB colors which is another can of worms because the scientific LAB space is not the LAB you'll find in Photoshop.
Broad topic, and then there are clients who will view your results on an uncalibrated display one day and tell you it's too dark, and the next they'll look at it on their mobile and tell you it's too bright and could be less saturated :D
I have worked in pre-press for some years and looking back I wish people in all places of the production chain (software vendors, too) would care about this today as people did 20 years ago when they printed stuff on paper.