What makes a T3 better than a T4 offroad?

A mate at work and I were discussing 4x4 or AWD systems and wondered, as both the T3 and
T4 have the same system (viscous coupling) what is it that apparently makes the T3 so much
more capable?

Is it purely the lack of clearance on the T4?
Maybe it's that the T4 drives the front wheels as primary drive coupled with the engine being
up front??
I was arguing with him that a viscous coupling is a viscous coupling but is there a difference
between those fitted to each vehicle? I thought not but it is worth asking you learned folk!