My personal opinion.
I have ssd and hdd mixed setup.
OS, games and storage on different drives. When I upgraded my gaming ssd from 512gb to 1tb SSD i did it without any problem.
When I reformatted and upgraded OS SSD from 256gb to 2TB SSD did not installed any games again.
My current setup is 2TB OS + 1TB Gaming + 512GB for MSFS cache. All SSD. I moved cache to my old drive i had since i did not want to fill my gaming SSD space totally.
So TL;DR answer, in my opinion go with OS + Gaming SSD