UPDATE:

Here is the conclusion to the debug of my issue.

First off my reporting of only getting 50Mbps was misleading because I was using a USB ethernet adapter which was limiting my full bandwidth.  Once I used a USB-C based 1Gb adapter I was able to confirm getting 998 Mbs when my laptop was attached directly to the output of the Eero Pro 6E gateway, but then only seeing 1/2 of that 450-560 Mbs when connected to the 16 port network switch downstream of the Eero Pro 6E gateway.

After hours with Eero and SnapAV Araknis tech support ... Eero communicated that their solution "is best used with a fully unmanaged network (wired) switch".  In my situation I was using an Araknis Unmanaged + [Note the PLUS sign there] switch which has some smart features which Eero believes was causing the wired network to lose 1/2 the bandwidth.  Please note again that my issues were only seen on the WIRED side, the wireless side was always fine.  I also tested this with a TP Link Easy Smart managed switch Model number TL-SG116E.  The TP Link switch was also showing the same performance degradation issue as the Araknis switch.  There is nothing fundamentally wrong with either switch in OTHER configurations, but based on my experience here - these CANNOT be mated in combination with an Eero Pro 6 E router/gateway.

Key message here is "USE A FULLY UNMANAGED NETWORK SWITCH WHEN YOU NEED ADDITIONAL WIRED ACCESS DOWNSTREAM OF AN EERO PRO 6 E"

I have changed this network configuration now and am using a simple Netgear GS108 8 port switch connected behind the Eero Pro 6 E gateway and am getting fully bandwidth 980+ Mbps now in my client's setup.

Final reminder notes: I have clearly stated in my messages here that this is with an EERO PRO 6 E.  I have done many installations with the EERO PRO 6 and used this same Araknis 16 port switch and have not seen the same issues.  So if you have a different Eero model or setup your experience may vary.