Please take performance questions to the generic R7800 exporation thread, which is better suitable for those topics.
But shortly,
- yes, both master and 19.07 use ath10k-ct by default. For master I also build the mainline ath10k for comparison.
- Both 19.07 and master use DTS, which you can easily see from source code. Like I already said to you in my previous answer to you, there has recently (=this year) been some DTS work in master, so it is slightly different.
- DTS (DeviceTree) has nothing to do with 5 GHz wifi.
- There is not much real-life difference in performance between master and 19.07.