Thing is we never know what the future holds. All we can do is take a well considered gamble based on what potential seems to be there.
Weekes may be 4th in line today, but injures/form drops/transfers of others cant be predicted. Weekes may develop fast over an off season (it happens and he's young enough). He could end up filling a position we least expect and succeed.
The danger is always thinking only in today's perspective. That's there the mistake with Gutherson was made. 2015 season, we had Turbo, had expected to keep Foran, an aging but still serviceable Jamie Lyon and Matai, Parker, so we were well serviced with five eighth, centre and full back. Where does Gutherson fit in as possibly third of fourth in line? Move forward 2 years and we were without a 5/8 and struggling to get a decent centre pairing. And Manly have struggled in those positions ever since, and not to forget being without Turbo for 50% of the time.
Same issue could apply to Weekes. Manly in the past decade seems to think only of the moment. Today we dont need him. Tomorrow who knows. And its tomorrow we need to consider more. So we need to look at potential. Might fail, but we can afford that mistake if its small pennies for a year or two. Let them go and it could cost us a motza. Always best to keep an ace up your sleeve.