He can't tackle at centre so you want to move him to a position where he has to make more tackles?
Defensively it is a very different position.
Less lateral agility required (the more the better still), less pace required to close space (again, the more the better but usually opposition are slower and taking on smaller gaps)
But workload increases significantly both in volume and tackling more larger players.
Backrower also controls the whole edge a lot, often it is them who dictates if the half commits in or out (or gets stranded with two people running at them), which has a flow on effect to centre and winger positioning.
A player could absolutely be a good defender at second row but not centre. A very good defender at one would usually be able to be decent at the other.
Hard to judge for Talakai right now - edge would suit his lateral movement and pace more. I'm sure he can handle the contact though volume over 80 is a concern for me. Decision making? Has looked bad at centre but Wilton and Moylan both being weaker tryline defenders have contributed to that also.
You may well know that and are just making a joke, but for the purpose of discussion and why it might work I've typed it up anyway