I agree it's a partnership, idea-wise, but I always pictured Egon as the builder, even in the two live action movies. He's the one with the PKE meter. In part two, Egon has the Giga meter. He's got the best toys. He has the negative emotion detector in part II. Also, we see him tinkering with a neutrona wand while they eat the Chinese food. He's also the one working on the slime blower in part II when Venkman calls. Stantz I always pictured doing the day to day mechanical stuff (like fixing up the Ecto-1) while Spengler handled the Ghostbusters' "little toys."
Yeah, same here, and that's emphasized more or less by the fact that Egon is made to be the scientific geek that he's portrayed as in the movies. And then the Ghostbusters video game has Egon give the rookie new toys to test. Also, isn't he also the one warning the dangers with the containment unit and the crossing of the streams? That makes him come across as someone who knows the technology best. If Ray is technically building things, it's likely by Egon's designs and the theory of how they should be working.