Out of curiosity, how can one mainline be the benchmark for all other mainlines when there are core differences between them and their faction designs?
Volksgrenadiers are supposed to be more efficient than Grenadiers because Volks are the backbone of OKW and are supposed to operate largely on their own, while Grenadiers are supposed to be supported by excellent team weapons. Infantry Sections are supposed to be more efficient because they are the faction's strong point (though yes, bolstered IS are a bit too efficient now). Their cost efficiency can not be directly compared to Grenadiers because they serve different designs. There are many more factors that define what the power level of a mainline is supposed to be. It's more than a straight comparison to another faction's mainline.
I do not to pretend to be an expert on this and since you have direct access to Relic maybe you should ask them.
I can respond on how I understand it which might or might not be accurate. First you create a baseline which in this case is a long range infatry like Grenadiers. Then using it as your baseline you roughly estimate what number you new unit should have and then you test your new versus your base line. Once you are happy with the result you estimate the cost compared to you base line.
So you unit does not have to be on the same power level. IS are comparable directly to grenadiers because they similar units, so are VG that have not been upgraded. Once upgraded the VG are no longer long range infatry but all range infatry and thus one should either come up with correlation of this type of infatry with the base line (for instance according to Relic CQC infatry 0.75 cost efficient) or create a new base line for this type of infatry.
The idea is not that everything should be of the same power level but that everything's cost efficiency should be comparable to base line. One could argue for instance that in the original design Riflemen where design to be more cost efficient than Grenadier because grenadier had access to more cost efficient support weapons. So when riflemen proved to be problematic Relic move the HMG to HQ to make Ostheer support weapon even more cost efficient.
Imo we are getting off topic now, if there is a need to continue this we can do it via PM. Imo you should actually directly conduct Relic and ask for their input from the work they have done so far.