Websites with heavy use of websockets skyrocket CPU usage in Safari

As troubleshooting steps, I'd try the following:

• Test with another browser to see what happens. If the problem isn't repeated then you're starting to isolate the issue, although I would then try a 3rd browser for good measure to see how it also behaves.
• Boot into Safe Mode (see below) and test again with Safari

Boot into Safe Mode

Follow these steps to boot your MBP into Safe Mode:

1. Fully shut down your Mac
2. Restart your Mac
3. Immediately press the Shift key and keep it down
4. Let go of the Shift key when you see the login window (NOTE: If you have FileVault enabled you may need to log in twice).
5. Take a note of what happens (i.e. visit the sites again with Safari and try to replicate the problem)
6. Exit Safe Mode by restarting your Mac as normal
7. Test again when booted normally

Let me know how these steps went and we'll go from there.