Well there’s hi def, and then there’s HI DEF. Originally, hi def (ATSC 1.0) was 720p or 1080i. Today’s 4K HI DEF (ATSC 3.0) is 2160p, and with HDR in some cases. Some OTA does broadcast at 4K but usually only specific programs, and almost never with HDR.
Once you’ve experienced, 4K HDR, especially on big screen, hi def is dull.