Burrows has played wing back less than 10 times in what must be around 150 career games. For the majority of last season, his first above league 1, he was very good in the main playing as left back. WB is different to FB. Burrows to be at his best going forward needs a partnership in front of him (See hamer last year drifting inside and dragging players with him), you don't get that as a WB, it would also expose more defensively, and the only real option for LCB is Ben Mee who you would want playing in the middle and not getting dragged out wide.
I have seen Seriki play wing back once under Hecky and he got slaughtered, albeit a few years back. Last year, playing in a 4, for the majority of his game time did well, taking into account he is a young kid learning his trade. He can and will improve and may one day progress into playing WB. Currently the evidence he can do that role is absent and people are guessing saying he can.