Spolsky's role is addressed in his blog post about The Time That Bill Gates Reviewed His Work. It's an interesting read itself, I recommend it.
https://www.joelonsoftware.com/2006/06/16/my-first-billg-rev...
tl;dr He wrote the spec for VBA, aka Excel Macros. It's not being in charge of all of Excel, but I would call that a pretty substantial contribution.
It is definitely not my point that Spolsky's role with Excel was unimportant. Hopefully, none of my comments can be taken as minimizing his role at all. I'm just saying he wasn't an Excel dev lead, which is a distinction that is relevant to this thread.
(Microsoft has a more complicated PM scheme with I think two different kinds of PMs? So I can't speak to exactly what Spolsky's role was there. It wasn't a small role, but no, I don't think he led Excel development.)