To add to this:nice edit.
luckily I caught your original response. which still does not answer all of the questions raised.
What does SUC vary on? What E1 jobs are there out there?
Firstly, tell me, if one has the option of a light PM, AI, light role, and SPIB SUC roles open to them (which most divisions do) how do people move battalions, or rejoin re-roled battalions if they have no experience in the new role? Perhaps, as arms-plotting demonstrated, one can move roles and pick it up, with some effort.
Secondly, how is any battalion's training programme so impenetrable? Arms-plotting again shows that units can re-role quickly, so why cannot officers? Light role BGs are very different beasts with very different G4 burdens to AI BGs.
Thirdly, what courses does a junior officer go through these days? Do orders and the estimate process change ? If someone could do step-up in a CSS HQ, how different is the process in a GCC HQ? What set-up do all of the officer education courses use?
And lastly, with the current officer career model, why can a major not transfer and have a successful career? I know a few, including those achieving starred rank.
Officers who end up in the group routinely command regular units having last served in that role as a first tour Lt. If you can do 15 years away from the regular army, in a completely different role and under completely different circumstances regarding funding, G4, admin, etc. and still command a regular unit then you can probably jump across at SUC with a bit of work.
I think cross-decking SUCs will fail a decent chunk of the time but some people will be successful at it.