Cygwin X - Vast performance difference between X-over-ssh and xdmcp

[Jim Garrison]

This may be off-top, please advise if so

TL;DR

Running X clients (pyCharm, git gui, Eclipse) on a Debian 12 system with 
Cygwin-X as the display server exhibits vast performance differences 
depending on how the X session is connected. X-over-ssh is sluggish and 
laggy, but the same apps are lightning fast in an xdmcp desktop session.

Details:

Cygwin/X Server: Ryzen 9 7940HS, 32GB RAM, Windows 11, fully updated
Client: Intel i5-1135G7, 16GB RAM, Debian 12, fully updated
Network: 2.5GB ethernet (verified with iperf3)

The speed difference is stark.  With X-over-ssh Eclipse is unusable, 
PyCharm barely so.  When running in an xdmcp session both are blazingly 
fast with no detectable lag.

What would make such a huge difference?

-- 
Jim Garrison