I really like what the saints are doing. It would be great to see them win a flag. I hadn't even considered the French Foreign Legion comparison but it's a great one.
As for whether they have it right or not, only time will tell, but I don't think it'll be right for all teams if it works.
Its not a new concept, see South Melbourne of the 1930s:
:https://australianfootball.com/articles/view/the+foreign+legion+at+play/1973