You are right that having higher extensions is not on first glance effort, but on second. Consider the extension needed to move 5kU around => Indu bot control, glider control, navigation Nexus.

You don't need to be able to move anything better than sequer, but you will not be able to finish this assignment in 1h when you lack extension to move Lithus/Scarab. In fact I would say, every sane person aborts this assignments, when not able to use a bot with more than 80U.  So in fact this assignment requires some higher extensions, but none production related in order to do it proper.

My point is why should a production assignment perform better for hauling skilled agents, than for production skilled agents? It is safe to assume that a typical production agent has at least 5% less speed due to nexus than an haul agent for the first 1 million EP.

I'm with Goffer here. Production assignments really should get an overhaul. The required volumes to haul are simply outrageous on beta islands. As Goffer mentioned: nobody with a sane mind will go for them on beta.
That's why i assume you Dev Zoom haven't done them either . I can't understand why you try to neglect the influence of extensions on difficulty and/or efficiency for productions assignments. You've created a game with competition as its core yet deny the associated human behaviour quite often (aka min/maxing). 2 things have a major part in the outcome of every endeavour in Perp: personal *skill* (whatever that might be in a specific situation) and of course extensions.
There's no reason that extensions should have no influence on assignments.
Production assignments are just not a viable option given the state they're currently in - no matter if they're matching your vision of how they should be or not.
Just reduce the required hauling volume by a good portion and they're fine.