Very poor download speed using excellent wireless connectivity

5Mbps is what Netflix recommends for HD streaming. I like to see more like 8Mbps for a glitch-free experience. In the past, I have streamed at 1Mbps as have others on the forum. It's acceptable if it's all you have or there's a show you can only get that way.  Largely static scenes can look reasonably decent.  (But when I was young, I used to watch Over The Air TV from hundreds of miles away so I could get up to 5 channels so perhaps I developed low standards.)

If I understand your question, you would probably have to try another ISP, for example a hotspot on your phone, if you think Spectrum is a problem.  But many phone hotspots are quite limited.

Bewildered_Bob I would start with doing an Ookla speed test and see what your upload/download speed is through your network.

Bewildered_Bob 

That is a pretty low download speed for Spectrum.  Even their slowest speeds (Spectrum assist) are 50 Mbps which you should be getting roughly 75 to 80 percent of that guaranteed.  Typical internet packages from Spectrum are 100 to 200 Mbps with 500 and 600 now common for their packages.  Check to see what internet plan you have to see what speeds you should be getting.  They guarantee 80 percent of that speed, whatever package you are signed up for.  I would also contact Spectrum to have them do a test on your line to see if noise or the signals are messed up creating issues.  I had something similar a couple years ago, where the signal noise created issues and it turned out it was a broken pin on Spectrum's port that controlled the network in the area that caused intermittent issues.