Karnov is a much badder dude.
Karnov was popular enough in its time for Data East to make its titular character their mascot for several years, having him make cameo appearances in several games. And, as a mascot, he's a pretty good one. When you see an overweight, washed-up Rushkie who breathes flame, you remember him. While the game is fun in short bursts, the frustration level can be so high in some of the later parts that, combined with its general flaws, it's perfectly understandable to want to put the thing away for six months or so.
A mediocre arcade port fondly remembered more for its main character than any actual quality gaming.