Performance is often an issue on the Raspberry Pi because of the low amount of memory. Pi-topOS is optimized to work best with the pi-top apps. You have a number of options available to improve performance:
1. Change the memory split between cpu and gpu. The gpu memory is set to 256 on pi-topOS. If you reduce it to 128, you will give the cpu more memory, but some programs making very extensive use of the gpu might just fail.
2. Run pi-topOS without the dashboard, which uses a significant amount of cpu time and memory. Open a terminal and type:
sudo systemctl disable pt-splashscreen
sudo leafpad /home/pi/.config/lxsession/LXDE-pi/autostart
Put a # in front of the line calling pt-os-dashboard. Then shutdown and reboot your pi-top.
You can always start the dashboard again opening a terminal and typing:
3. Use standard Raspbian Stretch on a separate SD card for critical apps. This is my preferred option. Stretch has the latest Chrome which runs a bit better. For instructions, see github.com/rricharz/pi-top-setup