We have hotspot on mikrotik that is connected to freeradius. I have test it and have slow browsing when logged on hotspot, when access directly have much better connection, have try it with android speed test app. When I am on hotspot I get 1Mbps, when on normal ap then get 4Mbps, they use same connection to get out on internet.
I will give you access to mikrotik device so you can make test.
You need to provide working solution on our device, script how to set up hotspot to work fast, and technical explanation of solution for problem.