It's not weaker than it should be, just weaker than you want it.
Output is limited by law. The Cisco is as up to date as you
can get without switching all your devices to AC as well as
your router. USB adapters are available but probably not on
the Roku.
One possiblility (if it's not Charter) is to get a set of the wall
plug in internet thingys. Plug one in next to where the router
plugs in and hook it to the router. Plug the other in next to the
Roku and hook a wire up to it. Or, it can be plugged in anywhere
in the house. It runs the internet over the electritic wires.
There's also wireless extension devices we talked about when you
were choosing the Cisco but you didn't want to fool with that.
Checked newegg, looks like they're all out of stock.
"Powerline ethernet adapters" was the search term I used.
Oh well, sometimes you can reposititon the router for better
coverage. Higher is better.
You could get a long cat 5e cabler and strectch it to the Roku
from the router to see if it's Charter or not but you probably
wouldn't want to really wire it up permanently.