Yep they were the original "killer apps" and still are. They are the reason that PCs gained traction in businesses in the 1980s. I helped my chemistry teacher in High School back then to use Visicalc on a TRS-80 as a gradebook. Almost anyone who has used a computer for work has used a spreadsheet for something, whether managing simple lists, or something much more complicated.

I would argue that the compiler is the most important computer program.

Or maybe that it doesn't make that much sense to look for a most important program.