That's very odd that they're able to reproduce the performance issue yet no bug. Even odder that your processor appears to exceed ArcGIS Pro 2.4 system requirements—ArcGIS Pro | Documentation but tech support is telling you it doesn't. Did they cite some other documentation to substantiate " they claim my CPU speed is a slightly below spec so I am at a stand-still with regards to technical support". If there are different vendor standards the delineate when Pro will or won't be supported based on processor that's not already in ArcGIS Pro 2.4 system requirements—ArcGIS Pro | Documentation I'd love to see it. When you say stand-still, are they wanting to close the case because of your CPU (which appears to meet specs)?
This is opposite of my experience with tech support, they move cases to bugs quite quickly and never tell me something is unsupported that actually is. What I think is going on though, is something similar to a case we had where we were told the minimum requirements were what is required for the software to start. So what you could be hearing is "yeah, your CPU allows Pro to start, but loading a project? Good luck!"
Let us know when/if you move this to a bug. You will be one of the rare few people that actually got tech support to reproduce one of the many elusive performance problem that seems to be universally reproducible when reading GN posts but not in an ESRI lab. You should get an award.
FWIW I and many others experience the same issue when opening projects that have many maps, layouts, database connections, server connections, portal connections, or any combination thereof. Not only is opening the project slow, publishing is slow, opening a map is slow, running a GP tool is slow. Looking at traces and intercepts, I see lots of traffic going to every connection in every "element" despite the fact that I have only one map open.
Your issue may be related to one or some of the very many issues mentioned in ArcGIS Pro: 2.4.2: In general, ArcPro has less performance than ArcMap, and possible https://community.esri.com/thread/242321-arcpro-242-arcpro-is-much-slower-than-arcmap-in-publishing-...