This isn't an argument to "justify paying the leadership more". That's backwards. This is an argument to say that when you're a board member trying to fill a leadership role, it might be worth it to spend a good amount of money to bring in people who would otherwise never take the role.
If you want a line-worker argument, it's similar to when people start trying to outsource software work to cheap firms and are then surprised when the results aren't satisfactory. Bring in line workers (software workers in this case) who cost more but are better and you might have better end results.
You shouldn't just pay the outsourcing firm more money and expect better results. In the same way you shouldn't "justify paying the leadership more", you should find leadership who are worth more money.
In both cases, it's possible you find the holy grail of someone wiling to work for the cause for little money and are also talented, but it's much more difficult.