Correction about trains. We use travelperk successfully, trains used to be a major gap but recently
they finally started to offer trains. Fully covering Germany (DB), France, Spain, Italy, Eurostar... You can book from within the platform and see it all in the same invoice which was a big upgrade for us... As far as I checked other tools like Concur and Egencia don't have anything close. Egencia actually redirects you to deutsche bahn making you leave their platform!
You made me laugh with the Concur story
it's so true! Super clunky and old, employees use it only cause they are being made to not because they want to, that's for sure.
There are still some small gaps in the tool (you mentioned a few) but all and all it's a big upgrade from what you are currently doing and much better than the traditional tools/agencies
hope this helps