Often, the picture on my 75" Sony set is poor due to LOTS of Compression by Spectrum!
Frequently, Local Channels look excellent OTA but poor (Visible Scan Lines) on cable. Cable-only channels also, at times, exhibit the same high compression effects.
Other times this effect is not present.
Spectrum is trying to push 6 lane freeway traffic down a 2 lane country Road!!!
What you are describing sounds like an SDV, switched digital video issue. SDV is a process where cable companies put channels, like the smaller sub channels, on SDV to save bandwidth and to add more channels. Every time Spectrum can reduce one program's bandwidth by 50% they can add another program at the same reduced resolution on the same shared channel. The bandwidth is then shared and when someone in your node tunes to the second channel another slot gets filled. You will often notice the loss of digital resolution when you're comparing a seldom-viewed program source off-air against its "On Demand" or SDV cable offering.
I understand how it happens but that doesn't mean it is accepable.
The compression frequently is visible on the local NBC and CBS channels, which, I would expect, are always sent to all local nodes.
This is a rolldown from the cable company offering higher internet connectivity speeds. As more bandwidth is dedicated to IP traffic, the cable company must make do with what is left over for video. That implies that video will be compressed (lower bitrates, not necessarily lower definition). It will look inferior when compared to an uncompressed ATSC over-the-air signal.
But your over-the-air broadcast picture quality may suffer, too, as a result of the broadcast spectrum re-packing. I have read that PQ has degraded quite noticeably on over-the-air stations which have entered into a frequency sharing agreement (one station took the money to go off the air, and now sends its signal out multiplexed with another station in the same market). OTA channels are still 6 MHz wide, but now they are carrying the video for two stations instead of one.
Many probably don't notice the drop in PQ, so they don't complain.
Just wait until cable companies start offering 4k more extensively...if you think 720p or 1080i are heavily compressed now then you haven't seen anything yet.
And that's being driven by the "Cut the cord" movement today, because they can stream UHD content to one or two personal viewing screens across their 30 to 100 Mbps internet connections. But each is a dedicated ethernet PTP data link, not a multipoint broadcast connection over cable.