Given that many people change from Silver to Gold on nights, and not status points, this is still a good offer. The only way you can not benefit from the lack of Status points is Platinum to Diamond. However, IMHO it is not worth the effort of chasing Diamond in Accor when other chains ( such as Hilton ) offer better value benefits at the higher levels. The other reason may be that Accor does not want to make Diamond status easily achievable ( I sense in a few years a change of benefits distribution )
This promotion is to fill rooms. and it may just work. If your "family" member has no status - its a win for both you, and the hotel, provided the "family" member does not "Rock Star" out the room ....
There are a lot of empty hotels and vacant rooms in most chains at the moment - look at the promotions on Secret Escapes and Travelzoo for examples.