It's hardly fair to look back with 30 years of hindsight and say that BASIC was more important to a company than SoftCard. Obviously, we know that now, but that doesn't speak to their specific situation.
I don't discount the importance of SoftCard, it was actually key in the development of the relationship between IBM and Microsoft in the 80s, but even more key was the building of the relationship itself, which was largely driven by Gates.
Allen's attitude at the time reminds me of software developer coworkers who over emphasis the contributions that software development makes. I can understand Gates' reaction - Gates' job was not any easier and certainly not any less important, so why redistribute shares?
Is that a mistake?