This operation typically takes around 70 seconds to complete on Tableau Server 10.3.
But in Tableau Server 10.5, this operation takes about 50 more seconds to execute. See images below.
I can't share the workbook or code being used here as its proprietary, but I can share you details about the server configurations.
The 10.3 and 10.5 servers have identical hardware. The most substantial difference is that the 10.3 server is running Windows Server 2008 R2 Standard and the 10.5 server is running Windows Server 2016 Standard.
To get the data onto the 10.5 server, I created a backup of the data on the 10.3 server and restored it to the 10.5 server. This is important because 10.5 might handle legacy data differently than the 10.3 server as it now has Hyper support.
It's clear that the responses from the 10.5 server are larger than those sent from the 10.3 server. In addition, the speed in which the 10.5 server responds is generally slower. Since the API can't make API requests concurrently, and the requests are blocking, every additional millisecond, not to mention seconds added to each request adds up to a slower experience overall.