My major OTA channels (NBC, CBS, ABC, FOX and PBS) are superb HD quality (1080 and 720). Those are the .1 channels. Their subchannels (.2 and .3) are 480 resolution - some are DVD quality, others inferior (almost VCR quality).
All my majors (TS or MPEG2) are better than cable or satellite (which are compressed MP4) and in most cases better than Amazon or Netflix. One only has to compare a show like “Downton Abbey” on PBS with any other source to see OTA’s superiority. Football and hockey on NBC (crystal clear and sharp) beat any sports cable has to offer for resolution and fluidity - not even a contest… The Olympics image on NBC was terrific (which was probably done through the Korean facilities which natively broadcast the Olympics in 4K)!
However what I’m talking about is the direct antenna feed to the TV, not Tablo. The Tablo’s feed to my Roku from the antenna is not as great as the direct antenna feed though quite good.
BTW the subchannels tend to broadcast older programs (from the 1950’s, 60’s and 70’s) and their quality will be inferior sometimes if those programs have not been reprocessed by the studio. PBS however (on their .2 channel) is showing many programs originally filmed in HD at a lower resolution and they still look quite good.