It may be a better idea to compare the ml consumed.
But you’re right. The VTC6 is not the best 21700 around. It’s not a bad cell, at least compared to many other 2x700s out there, but nevertheless it performs worse than the 40T and the P42a for example. And if your mod has a relatively high voltage cutoff, it may even perform worse than a 30T in that specific mod.
More so if the VTC6 is an older cell and/or lower grade.