It's a bird, it's a plane... it's Samson! Okay, you got us: he's not actually Superman, but from the way some of the characters describe Samson's previous mojo, he's not so far off. Saving his people, conquering enemies, fighting while totally outnumbered—Samson definitely was strong and skilled. Unsurprisingly then, a big preoccupation of Samson Agonistes is: what happened? The question isn't just literally how Samson lost his strength and wound up in prison, but also whether the fact that it did happen means Samson never was truly either of these things. Could someone with genuine strength and skill make the choices that he did?
You can't actually call Samson "strong" because he was endowed with this strength by God and didn't even have to work for it. He just has a superpower.
Samson probably was never as super-duper as he and everyone else has been claiming. He's just romanticizing his past life.