Back when SSDs were expensive and tiny they used to sell hybrid drives which were a normal sized HDD with a few gigs of SSD cache built in. Very similar to your proposal. When I upgraded from a HDD to a hybrid it was like getting a new computer, almost as good as a real SSD would have been.
I say go for it.
If it’s all Steam games then you could just move games around as needed, no need for a fancy automatic solution.
They eventually say that, yeah. But only after first saying a bunch of other misleading stuff.