You are absolutely correct.
Wikipedia to the rescue.
Now I know why I really hate SCART. Every time I'm in England, I always get my father's system tweaked when I'm there, and leave with no Scarts. He has an installer that meddles, and he always seems to go to the drawers full Scart cables, adapters switches, junction boxes etc and mucks things up.
Last time I was over there, I bet I took 1000 GBP of Scart junk to the dump!
If you want to do what you want you will have to build your box. RGB is not two way and can only travel in the direction of the set.
Adapters and switches can not pass RGB quality.
Just look at the disadvantages of Scart. On my visits to the UK, I KNOW I have run into every one of them.
It is supposed to be fool proof, but it is anything but, and there are now as you see a lot of irregular Scart hookups, to confuse everything more.
I hope you do not have to live with Scart another 10 years. I promise you, if you resolve never to use Scart again your life will be simpler and results.
better.
The EEC need to stop mandating Scart on everything. Then may be you could afford modern HDTV. That Scart nonsense is consuming a huge amount of money to no purpose.
I bet you will save money, if you come up with a solution that does not involve Scart.
Everyone reading this thread should look at that Wikipedia article and understand why governments and especially government Quangos should stay out of engineering issues, and let the market decide.
Emmigrating in 1970 was the best decision I ever made.