He was getting 300k per week from 2014-2017 and was putting on performances Ali Dia would be proud of.O'Shea and Brown never were integral part of United team, they were rotational players, it's but rich to compare them with Rooney.
Who cares if he did all that when up to the point of his decline he already had everyhing accomplished? Who should he prove anything else? GifLord and Black Adder or whoever from internet?
He lived his life the way he wanted and got everything he wanted, what's there more to ask for?
When Rooney got criticized by the media for his poor form he even tried to downplay it by doing the same thing you just did - talking about things he's accomplished in the past.
Remember that infamous guest appearance on the Paddy Crerand Show?