their confrontations with Hulk are the only yardstick by which they can be measured.
Surfer clearly is both powerful enough to take everything Sentry can conceivably through at Surfer and to take out Sentry with his own attacks (having destroyed planets and created blackholes with gestures, what would he achieve with serious effort?).
even if you consider WWH to be exceptionally strong, unless you classify him as Celestial level, he sure doesn't bear comparison with Tenebrous or Aegis.
Surfer attacked and took a beating from both of them. 2 on 1, and he was both conscious and lucid enough to formulate a plan and then execute a manoeuvre that required phenomenal amounts of stamina and durability (enough to impress Galactus!)
this compared to Sentry basically emptying out and getting knocked out after a brawl with a Hulk who wasn't even particularly interested in fighting him, nor angry with him even after the fight.