This is it. This is the actual crux of the issue. "Age of Consent" really isn't (or at least shouldn't be) about how old you have to be to be "ready for sex" but about drawing a line between children and adults to protect the former from being abused by the latter. There is a categorical difference between two 15-year olds like you said, getting handsy with each other and a 30-year old "getting handsy" with a 15 year-old. The first one is relatively normal human development, the second one is objectively sexual assault of a child.

The age of consent laws are flawed and do lack nuance largely because the bar is set too low. There should be gradations to it, but they should be going in the direction towards older, not younger. As one possible example of adding nuance to it, making it illegal for a 30-year old person to have a sexual relationship with an 19-year old person, but not perhaps with a 23-year old. Some of the so-called logic in the OP screed is sound, but because the person writing it still has a specific conclusion they want to reach, they can't see that if followed to an unbiased conclusion, it's advocating for an AoC that is higher than 18, not lower.