The law of supply and demand. They are not overpaid as there are very few people able to supply themselves and demand is high because its fun to watch the footie.
This is moral because it is based on voluntary exchange.
There is only an arguement for under not overpay unless you are the oe paying the wage
If someone else is paying too high of a way they bare the cost of doing so.
Someone's worth to society is very hard to quantify, boardrooms would have huge incentives to downplay their employees worth to society to lower their variable costs
Our markets need to be pragmatic not idealistic.