Obviously a show called "Seinfeld" rests on there being a Seinfield. But, no, he couldn't have been a potted plant -- he had to be able to play his role. That was easy compared to what the other actors had to do, but it still required some acting ability. He was quite candid in admitting he didn't have much of it --that, for instance, only his off-the-screen friendship with Julia Louis-Dreyfus allowed him to act out his role vis-a-vis her character.
but for them to shine like they did on the show, the potted plant was needed.
No, you're playing Ashokan according to the script. Not the same thing at all, even if you're writing the script. You have to stay in the character as called for by the script, and you have to be careful not to be the "real" Ashokan when that conflicts with the script. It's easier to play than Roger Goodell, but it still requires some ability.
