There's one little difference you are apparently aren't seeing (irony of which should be noted), Burrow had obvious talent you could see even his first year as a starter at LSU, offensive player of the week twice and leading them to a 10-3 record. His talent was on full display by his second year as a starter that translated to a national championship, Heisman trophy, a can't miss NFL starter, first overall pick, and a highly successful career so far with a near 70% completion percentage 4000 yards a year. Mertz has already started 3 years and is hot garbage.
If you are holding out hope Mertz becomes the next Burrow, you'd have better luck hoping the Fed Rate drops to 1% next year.