I said this earlier but I am going to reiterate things again.
You guys seem to be spending a lot of time and energy arguing whether it is an Intel vs Qualcomm modem issue or a bad antenna design. The fact of the matter is that NO ONE here, including myself, is qualified to definitively say whether the issue is caused by bad hardware, software, or a combination of the hardware and software working together.
Personally, despite it having a less performant antenna design I feel like it is more a software issue because as many have reported Airplane mode, Restart, or Reset Network Settings temporarily fixes the issue. If it was completely antenna design problem then it wouldn't work at all.
However, frankly we are wasting a lot of time posting here how many bars you have and how fast are your speedtests. While helpful to see if you are experiencing major performance degradation you should really be focusing your energy on working with AppleCare support. This is what I am doing.
The best way to solve the problem is to work with AppleCare to get the baseband profile installed which enables debug logging for cellular.
https://developer.apple.com/bug-reporting/profiles-and-logs/
Then you will need to reproduce the issue and create a sysdiagnose which compresses a bunch of logs together. Then get these files over to support who then send the files to engineering. It is only then that engineering can finally take a look at the hard data and dig through 1000s of lines of logs to try and figure out what is the root cause.
Then after root cause is found then they can work on writing and testing a code fix.
Spend less time doing speed tests and more time working with AppleCare to gather logs to send to Engineering!