The one with highest rank, and the first in alfabet will take the overall lead. Silly but true. The subordinates only affect their own units.
I will use Rommel as a division commander as long as I can. Why? Because he will gain even higher skill level that way. You don't seriously need any more gallant guy than Liebermann or von Fritsch to lead campaign against Poland and Yugoslavia. Blaskowitz, von Arnim, Geyr von Schweppenburg, Hausser and Falkenhorst in my game have advanced to level 7 while leading divisions or corps.
IIRC the commanders you are naming have a skill level 4 at best and some even have a lower skill. It’s a bit of waste. Though your high level commander gets more experience quickly, your lower level commanders don’t, cause they are higher up the ladder and earn skill far more slower. You probably end up with a few high skilled commanders and lots of “low” skill commanders. Just a though…
Besides the leaders and traits link in my post of 30-10-2014, there are quite a few strong arguments not to assign him at divisional level but at least at army lvl:
Traits trickle down and the amount of commanders with more than 2 traits and a high skill level are limited. When assigned at army lvl, a maximum of 25 divisions benefit from his traits!
The skill lvl of an army commander increases org levels by 1% per skill level. In Rommels case that’s 5% for 25 divisions. This indirectly also means a faster org recovery after battle!
Assign your highest skill lvl commanders to command an Army Group. Per skill lvl they reduce supply consumption for their subordinate units by 5%! A lvl 5 commander reduces this by 25%! That’s a lot of IC that doesn’t need to be invested in supplies.
If you wanna increase the skill level of commanders, you can also assign them to support attacks or add units to their HQ. Using this method, Rommel usually has a skill lvl of 6 or 7 by the time I attack Russia. So basically I get the same results as you do. You can add any unit to a HQ but a Germany I usually add the LARM units available at the start of the scenario to my Army and Army Group HQ’s. This way I don’t have to upgrade them to ARM and still get a very good use out of them. Especially for the commanders involved and when HQ speed starts to near 8 mph. But you can add any unit with combat width to an HQ.
If you wanted to do something similar, at the start of the scenario I set up my OOB in such a way that it’s ready for the attack of France. So my OOB in the east has one Army Group and five Armies. In the West I have one Army Group and one Army. For the attack on Russia I only need one extra Army Group and Army.
Anyway it’s your game…