HTOP is just CPU. It is more than likely going to be bandwidth related (and if I had to guess, on the wifi side of things if your internet has plenty of upload speed).
There are also other potentials, routers have a lot more than CPU to worry about, NAT and connection/session tables for instance, but any modern router (or any made in the last 10-15 years) can handle a lot of either one, with the exception of some buggy firmwares that have come out and eventually gotten fixed. If your router has a CLI interface you can access, it is most likely a decent enough one to handle all of that though, so I go back to wifi bandwidth being the main suspect.