Thing is, it's more than just "a few cm". More like 10 cm against the best sides:
De Jager 2.06
Etzebeth 2.04
Whitelock 2.03
Retallick 2.04
I reckon 4 inches is significant.
Yeah, sure agility, speed, jumping ability and ball skills are important. But I dunno whether Lopeti Timani has special talents there anyway. Certainly wouldn't match someone like Whitelock for that.
Essentially if he was picked as a lock, he'd be a Brad Thorn type to add power in the scrum and an enforcing physicality. You'd sacrifice something in the lineout. (We've already been doing that with a 6'8" non jumper, and Timani might even be better than him in the scrum).
But there are also some good genuine locks coming through in Enever, Coleman, Arnold, et al.