Sentry was at times portrayed as basically a blonde-haired, flying brick Superman clone. Some Superman portrayals are on or above some Sentry portrayals.
But Sentry's high-end is, of course, much higher. It's pretty hard to rate his showings and use them to compare to other heroes because you never really know how much of his true power is at play in any given showing. In his way, sentry's a bit like the Hulk that way, though perhaps even more variable given his true upper limits.
To be fair, I happen to think that there are a lot of Superman portrayals where he might do to Terrax exactly what the sentry did to him. Superman's power levels are fairly dynamic in their own right, though again, typically without anything like what was often shown to be the Sentry's top end.
I think Superman is typically the most powerful single character here, with the most upside potential to dominate when feeling frisky.
But again, that's me rating fights by the comics and comic conventions.
If we were more realistic about it, we'd have to decide whether we can simply infer super speed reactions and movement to both the Heralds, or whether the DC duo could speed blitz them. It's shown that Stardust can at least be put down temporarily by physical force; and once's he's down, the DC team could figure out what to do with him between some kind of use of Superman's heat vision and Shazam's magical abilities.
If the Herald's can't be speed blitzed, then the next decision point would have to do with how much versatility with the power cosmic the Heralds really have. Terrax in particular tends to prefer fairly concrete applications, but it may be true that in theory, both Heralds have as much versatility with the Power Cosmic as the Silver Surfer, if less skill and power. In such case, the number of ways the Heralds have to realistically insta-win is almost endless. Raw power isn't really the issue if we get realistic, not given that they each have at least some fairly health fraction of the Surfer's power level with the PC. That's more than enough.
That's how I'd analyze the fight if I were being more realistic about it.