In today's economically rationalised world, almost every position in a company is important. If it wasn't, they wouldn't pay for it. Saying who is more important to the process is somewhat meaningless - wages are generally aligned to how difficult it is to replace a person's skillset.

The core activity of a band is making music. The bottom line can be helped a lot by marketing. Other roles may be very important to allow the musicians to focus. Sometimes musicians need to be kept sober or made to practice more, with which others can help. So other people can make value in a band and deserve to get paid. But take away the musicians, and you have absolutely nothing. Plenty of people have made good music without lots of managers over them. In that specific sense, musicians are the most important part of a band.

I think that's a flawed analogy, because the band is set up to sell the specific art of the musicians. Software companies are set up to provide a product using the craft of the programmers. It's a lot easier to keep the same flavour in your product if you have to replace a lead programmer instead of a lead singer. Programmers in companies don't do the equivalent of "I'm going to change tack and do a blues album this time".