Thinking in NRL terms not Fantasy.
Roosters are much better with Walker at 6 and Manu in the backline than with Manu at 6 and Corey Allen in the backline.
I think Walker is highly rated enough that they won't banish him to reserves for too long.
Thinking post origin, who are the best 2 centres going to be? Jack Bird looks like 1, and I guess the other could be one of several (Manu included) who end up going on a hot streak of form