Interesting. My 2019 AMG wheels are 19”” the steel spare is 18”
It took me a while to remember where the plug to lower the spare was located. I always carry an extra long socket wrench to undo tight wheelnuts and changing it wasn’t difficult.
I am also covered by MB breakxdown assist which, as you say is subcontracted to RAC. However, the MB, subcontract required RAC to tow the vehicle to MB to get a replacement tyre fitted even though I was paying for the replacement tyre. It was 25 miles in the wrong direction and MB weren’t even open.
Luckily, I also have Nationwide holiday cover which includes breakdown insurance through the AA.
A complete contrast. AA asked me the make of tyre I wanted and collectedit on the way out. The driver pinned his location to my phone so that I knew exactly where he was and his ETA and replaced on the tyre at roadside.