Honestly I'm still reeling at the GotG characters being described as "interchangeable."
"One-dimensional" is very much subjective, but "interchangeable"?
It comes down to personality types, and filling archetypes in the story. In Star Wars, you've got a collection of markedly different personalities.
Luke: wide-eyed, naive, idealistic, impetuous youth ready to take on the world and thirsting for adventure.
Leia: stern, focused, goal-oriented, responsible, passionate leader.
Han: surly, cocky, cynical, joke-slinging, loner, rogue with a dark past but a heart of gold.
C3PO: nervous, chatty, and effete.
Chewie: big, lovable, mascot character that's secretly pretty dangerous.
GotG on the other hand, its characters are more like:
Starlord: plucky, cocky, cynical, joke-slinging, loner, rogue with a dark past but a heart of gold.
Gamora: surly, cocky, cynical, joke-slinging, loner, rogue with a dark past but a heart of gold.
Rocket: surly, cocky, cynical, joke-slinging, loner, rogue with a dark past but a heart of gold.
Drax: surly, cocky, cynical, joke-slinging, loner, rogue with a dark past but a heart of gold.
Groot: big, lovable, cynical, mascot character that's secretly pretty dangerous.
This is obviously a little reductive and there's some nuance in the margins, but at their essence, each character is roughly the same in their disposition, personality, and M.O.
When I brought up the straight-man, comic-man duality before, you usually have the comic-man do something silly or ridiculous, and then the straight-man riffs on it. Either to roll their eyes, or point out how ridiculous they are, or provide some kind of reaction to give the comic-man something to keep working off of. And when I say the characters in GotG are interchangeable, it's because of specifically things like this, where every character is a straight-man, and every character is the comic-man at random in any given scene. In Star Wars, Han will say or do something outrageous, which will cause Luke to go *gasp* or cause Leia to roll her eyes. On occasion there are role reversals to mix things up, but that's the overwhelming trend. That's their roles and personalities. But in GotG, any given character will do something Wild and Crazy and everyone else will either join in or do a straight-man bit, basically at random. Drax standing still and pretending to be invisible while other people look at him like a crazyman, you could have had Starlord, or Rocket, or Groot do the exact same gag, and it would have made sense/not really skipped a beat.