So I’ve been reading a few more Casca books. During one readthrough, it hit me: Casca is basically a sword and planet hero (think John Carter and knockoffs of that). Sword and planet heroes tend to start their adventures by getting some sort of anti-aging/immortality treatment. Either because of this or just from some intrinsic advantage (ie, “low gravity), they have just enough of an edge over their opponents. Their adventures are either standalone books or arcs that center around exotic set pieces.
Casca? Cursed to be immortal and gains rapid healing. Advantage over his opponents but not an overwhelming one? Of course. Standalone books where he’s in one (pulpish popular) “exotic” historical period after another? Exactly. Now, I don’t think this was intentional on Sadler’s part. But it still comes across that way.