^^^ That right there.If it's a game that's not played often, the files are likely to not be in the Optane cache anyway, especially for the lower-capacity units.
It is just a cache.
Benchmarks and 'OMG! Fast boot time!' are poor indicators of actual user facing performance.
If we were talking about a database server, and the cache held the most accessed stored procedures, then sure...the Optane is a good choice paired with a 4TB HDD.
And it was designed for that use case.