Phew... I know exactly what you mean, we are currently building in Munich and I nearly fell off my chair when we received the surcharge offer from our construction company for the things selected at Richter+Frenzel (which were only furniture and fittings). And what upset me even more was that I found most of the items really ugly in the showrooms and qualitatively more on a Roller level (especially those ugly wood decors that just scream "cheap" and are supposed to cost €2,500).
At the same time, my parents-in-law had their entire bathroom renovated in Lower Bavaria for our "surcharge," including gutting, new underfloor heating, completely new tiles, shower, bathroom furniture, etc.
Honestly, I think it's pointless to inquire with two or three other wholesalers or sanitary suppliers, they will all be operating at the same level. Either bite the bullet and take the golden bathroom apple or do what I would have done if we weren’t tied to our general contractor and that lousy company from R+F when it comes to the bathroom: find people in your circle of acquaintances or friends who are handy or know someone who is (for me, that would have been my cousin and his probably 30 handyman friends) and have at least the bathroom furniture and fittings installed separately by someone like that (if I didn’t know anyone, I would have already checked MyHammer and bought all the equipment online).
For a 5m2 bathroom, I would probably even consider trying to tile myself with help simply because the prices here are so outrageously high and you currently have to wait forever for anyone to even show up. My godmother has been renovating her small bathroom in Ottobrunn for over a year (through a general plumber who does everything) and she is desperate because either no one arrives as promised or something is once again not deliverable.
I’m keeping my fingers crossed for you!