Edit: wrote all these trash without realizing it's a bot necro
Medieval army rarely have the kind of formal heirachy that we have today. An army led by a king naturally follow the King, and the Dukes and counts and marsques leads their own army which answer to the king by feudal obligations either command their own as a separate allied army or be subcommaned by their direct liege according to their individual duties, ties, etc.
And the Empires relations are no less complicated. For example, in Ludwig's folly from 8th edition empire army book, it was said the grand master of the everlasting light refused to aid him when his demand to command the entire army was denied, leading to ludwig's humiliating defeat. Now, based on RP 1st and 4th edition Enemy Within campaign, Luswig was "merely" the count/chancellor of the Oster market, not an elector count at this time -- nonetheless it shows the difficulty to regulated commands within the Imperial armies.
It is far more likely the military would be led by leaders based foremost based on their political power than ranks. A poor Baron with a small fief would lead a regiment as their "captain" while a rich Baron with command over a number of regiments might be a general in smaller engagements. Such as the regiment lists in 8th edition rulebook about Mordkins invasion shows (boghafen hand gunner or something).
Some provinces might have a formal ranking system, we know that Reikland has several marshals, Reiksmarshal prominently, and then the Huntsmarshal (but maybe creates just for Wulfhart?), Middenheim has three Midden marshals, Talabheim has a marshal mentioned in the Sigmars Blood campagin booklet (I think he was just called a Grandmarshal but I'm not sure), and so did Nuln in the Drums of War campaign, and Oleg von Raukob from Mordkin's story. However, Blucher von Vincke was also a Grandmarshal of the Reikland in the Background book Empire At War, and he was a contemporary of both Hellorg and Wulfhart. So multiple marshals can exist within the same province who might be responsible for different spheres of command like the Reikland, and the same spheres like in Midden land, or only one may exist in some other provinces. It's even possible no marshals exist in some provinces at all.
It is therefore more useful to simply treat the hierachy as a rough guideline, with Generals representing anything from an Elector Count, a Duke/Graf/Count, or even a very powerful Baron/Viscount ect. Captains may therefore be anywhere from a battle hardened veteran to the sons of powerful nobles, who themselves may have different titles like colonels (at least one mention in RP4E), captains, or even just addressed with their noble rank like Sir, Baron, etc.
Sergeants as far as I understand it would be mostly commoners, a position perhaps too lowly to be considered by any self-respecting gentleman of the Empire. Tho it might be such that the 4th and more junior heirs of a minor nobleman may seek employment within a regiment simply because a lack of prospects.
