While overall I think the division template and equipment mechanic is VERY slick.......there's definitely some oddities about the combat mechanics that don't seem very well thought out. Either that, or they were conscious decisions made to nerf things like artillery, which would otherwise be properly balanced by a more realistic supply model.
"Combat time" and supply is one of the best features in Supreme Ruler 2010/2020: if you want to have doomstacks of artillery battalions sitting behind your frontline blazing away, you ALSO need stacks of supply trucks driving back-and-forth down the roads to supply depots to keep the ammo topped off. That can get VERY micro-intensive, but that game is more operational in scale anyway.
But I'd like to see "combat time" represented somehow in HOI4. In the 21st century US military we talk about "Days of Supply" (DOS). Frontline units usually only have 3 DOS, so past that "out of supply" penalties would kick in. You alleviate this by having logistics units that provide supply points (perhaps multiplied by the province infrastructure). So a logistics support battalion (and you should be able to add more than one) wouldn't give a % decrease to supply required, but be a source of positive supply points to counteract your supply consumption which is highest during combat, high during training, and low but persistent while static. If we could build "logistics brigade" templates and add them to provide supplies to our armies, it would help to represent the manpower drain of the "tooth-to-tail" ratio that is otherwise TOTALLY absent in HOI4, which is why as Germany you can field like 500 divisions of combat troops when historically Germany at its height had maybe 200.
I'm just not sure how to link supply production/consumption to industry, and do so without the supply depot nightmares of previous HOI games....
Hope I didn't derail your thread...
EDIT: Also, while I'm not knowledgeable about Model's use of artillery, the Soviets however definitely used division-level artillery formations to great effect. I don't think the game mechanics adequately support the tactics and organization used by what is inarguably one of the two most important land powers of the entire game:
http://soviethammer.blogspot.com/2015/03/soviet-wwii-artillery-divisions.html