I’ve never tried 4K streaming (don’t have the premium subscription), but 17.5 Mbps for 4K sounds like a joke. There are older 1080 sources (especially with grain) where you don’t want to go too much below 15 Mpbs on H264. Even H265 generally works better primarily on newer sources material (post 2005) and encoding high complexity older film with H265 is going to give marginal efficiency improvements relative to H264.
I’ve never tried 4K streaming (don’t have the premium subscription), but 17.5 Mbps for 4K sounds like a joke. There are older 1080 sources (especially with grain) where you don’t want to go too much below 15 Mpbs on H264. Even H265 generally works better primarily on newer sources material (post 2005) and encoding high complexity older film with H265 is going to give marginal efficiency improvements relative to H264.