Note that I didn't say it isn't up to scratch. I was referring to others in this thread who said the protocols were subpar. Although RDP still does not support full-screen use on, say, 2 out of 3 monitors in a multi-monitor setup (the 3rd screen being used locally) without the famous VMware Workstation hack.
RDP works well for me personally in a variety of use cases (albeit none of them are graphics intensive) - however, user feedback I have received especially from engineers and designers has shown that they are unhappy with it.
For example you cannot (anymore) use discrete graphics in an RDP session (e.g. in certain CAD or 3D software). I think this was under development but got removed, iirc. Other protocols like the one used by Splashtop do support this but in our tests RDP on W2k19 still provided higher fps and a smoother experience than Splashtop (with the downside that some software wouldn't start over RDP because it couldn't directly access the graphics card).
Are there any particular optimisations you do to RDP beyond what can be done in the "Experience" and "Display" tabs of mstsc.exe?