There are a lot of components to being a great boss. You need to be fair, kind, disciplined, organized, and a lot of other traits. However, generosity and other traits that help employees to get on their side is a great sign of a boss. A boss can do a lot with dedicated people.
I think a great boss shouldn't have to be generous to be great. Sure, generosity is a great trait and benefits the employees as the boss is generous and gives more for their effort, it is surely not the key to being a great boss. I think one thing cannot determine a great boss. There are many other qualities that may be present in a boss for him to be considered great. Generosity may be one of them but it certainly isn't the key to it.
It is okay for a boss to be generous, but a boss can also be overly generous. If this happens, then the employees may begin to take advantage of the boss because they know that they can easily get what they want. Being polite and understanding are they keys to being a great boss in my opinion.
It is nice to have a generous boss, but that isn't the key. Maybe generosity in a sense of being generous with thoughts, understanding, and things like that. A great boss knows what needs to be done, how to get their employees to understand and do what needs done, and how to motivate and encourage production. Maybe having incentives is great, but sometimes people will rush or do shoddy work to do things more quickly.