Actually Howard is the only one who actually has done anything meaningful.
While "space plumber" is great for a giggle it is actually rather crucial if you want to be in space for more then a day or two.
As for the others I know Sheldon has made three "great discoveries" that turned out to be so much hooey. The only one I can think of that actually panned out was the one the red-haired girl helped him with. Raj spotted a comet and I can't think of anything ground breaking Lenard has done.
In fact the whole show seems to be about the fact you may be smart but unless you actually stop playing and start working you never get anywhere.
I would say the show does well to explain class welfare for the elite intellectuals. We need rocket scientists....but the truth is....ninety-nine percent of them aren’t really needed much. So we employ them at odd jobs, pay them what they think they are worth, and just grin over projects that have no value.
I won’t dump on Big Bang Theory....it is a well written script and they have done some five star episodes (the comet-passing episode with the guys out in the foothills was a classic).
I can’t think of anything ground breaking Lenard has done.
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In a word....
PENNY.
In THEIR world, it is equivalent to 5 straight Super Bowls, a Perfect MLB season, a P that averages 24 K’s per game, a batter averaging 2 HR’s per game etc...