FCPX freezes 14-core iMac Pro on simple 1hr multicam project

I am running FCPX 10.5.

I have a brand new iMac Pro with the above specs. Only apple and adobe products installed.

Working on a simple timeline is fine. The moment I have a large timeline (half hour or more) FCPx behaves like i am using a 2015 Macbook. My CPU/GPU and disk I/O are all low. I am working with straight ProRess 422 PROXY footage 1080p. FCPx just cant manage.

https://discussions.apple.com/thread/250545184?login=true

The above thread is a similar problem. This iMac sits at the heart of our company and is only 4 weeks old yet it is now the bottleneck. How would you feel if you bought a Bentley that wouldn't go above 30mph after you put 5 people inside? Thats how I feel. Frustrated and ready to throw my £8000 paper weight out the window. This is now causing us to loose money as are projects are running past the deadlines and FCPx just doesn't work well with large timelines. Why?

I do not believe that this is a hardware problem since the system has plenty of resources available. I am more convinced that this is the poor development behind FCPx. Calling apple support seems useless because they hand you to a FCPx guy who tells you "I will send this up to the FCPX developers" then thats it. Nothing.

So now what do I do? Tell all the clients that are waiting for their projects that we are waiting on apple to fix our Mac?

I just feel ripped off. Yes I've reinstalled everything including catalina and now im lost. Anyone with any ideas please help!