Whilst Isaako has been horribly out of form this year, Corey Allan has done nothing even mildly impressive in his time in the NRL. He seems big and slow and just doesn't have the body for a modern fullback where agility is so important.
Isaako has had a lot on. It's his second year of NRL, expecation on him is higher, he's recently had a child and his father is dying. I mean, that would put anyone through the ringer. He appears very popular within the group, and you can't fault his effort to training and those aspects. This year is a write-off for him, but I think he showed enough last year that he is a first grader and I think he will find form next season.
From what i've noticed with players and having children, often the 'loose / badboy' type players become more consistent and better players when they have kids, whilst the hard working ones sometimes go backwards due to a disrupted routine. I think this is usually because those loose/badboy types have virtually no routine, then have a child forced them in to one. Whilst someone like Isaako who from all reports was as professional as they come and always did a lot of extras, now has less time / a disrupted routine.
Time will tell if there is any truth to the rumour, but based on what i've seen, I don't really like it.