Expected: The blueprint node Set Scalability Quality to Epic sets the quality to Epic
Observed: The blueprint node Set Scalability Quality to Epic sets the quality to Cinematic
Investigating the C++ code, it is calling Set Scalability Quality Level Relative to Max with a parameter of 0 rather than the default of 1. Either the behavior or the name could be changed to make these match.
Workaround: If you need this behavior from blueprint in the mean time, calling Set Scalability Quality Level Relative to Max with the default parameter value of 1 appears to set the quality to Epic as expected.