Does this apply to all switches?
No, rate limiting / traffic shaping is a thing but only on routers, higher end switches, access points etc, its not a feature on cheap domestic £20 L2 switches like you are using.
Example a hospital might have guest WiFi access but they wouldn't want all the bandwidth taken if everyone started watching Netflix on their phone so they could rate limit the guest WiFi to a set % of their total bandwidth.
In your case either something is broken, the other devices are doing something in the background which is generating traffic or you are misinterpreting the results some how.
I've tried another port on my sky router to share the Internet to the switch. It doesn't make any difference.
I think they meant unplug the switch and only use the ports on the router to see what happens without the switch.
EG PC in port 1 of router = 500Mbps
Then add a TV to port 2 = still 500Mbps on PC?
Add another TV to port 3 = still 500Mbps or drops?
500mb is reported in either device when checked using ookla speed test
but if you add another tv to the switch it drops or has it starting working correctly now?
TV firmware upto date, no sideloaded IP TV APPS, you aren't in a botnet?
Over 1.5 million devices in 226 countries have been infected with this malware so far
www.tomsguide.com