There have been several threads on that topic last summer.
They are not the first ones to share accounts and to say it openly, and it is considered as legit.
Sharing accounts is not fair, but what can be done about it?
Regarding the present topic, there has not been any official answer so far saying if it is legit or not.
Some people who are obviously making trophies unreasonably fast are regularly banned, and it is a good thing.
However the cheaters and exploiters represent certainly much less than 99% of the top 10 fortunately.