Many thanks for your replies and sorry for being a bit late catching up.
@Turisu: you are right, they actually have indeed. That I’ve somewhat painfully realized by now.
After all, I put too much trust in the correct result of having madVR converting it including the usual comparison sources and based all my arguments on that.
Hence the only reason I opened that thread here was because I felt stuck there with no explanation before Geoff_D luckily pointed it out.
So it seems to be a general issue depending on the target brightness mastering, but this thread here might still be interesting in terms of having a comparison with a 35mm copy one day to really be sure.
@Synnöve
You seem to be right as well, as of now I guess we can entirely forget the usual image comparison sites and methods which most of us are only too used to. 😦