So basically, these guys are better programmers than Oni.
That isn't all that high of a bar to achieve, given that Oni had
zero prior experience in programming and used this project more as a ways of learning about programming in the first place, instead of creating a fully functional and bug free game on his first attempt, ready for mass appeal. If I remember correctly, he even stated as much in some of his update posts
way back when the game was really in its early stages (this meaning only having mostly finished rogue and just barely implemented kitty).
That's not to say that he hasn't improved over the course of the development, just not by all that much because there was never really much
need for improvement. While the game ran mostly fine, bugs that he created also got stamped out (though sometimes he even re-introduced them and stamped them out once more) and with the game growing in complexity, he had to adapt, which leads to the code-revision in version 0.90 iirc, though how well that holds up I cannot tell as I have little experience in that field myself and am only relaying all the info.