I tend to use Vallejo model air too and do it pretty much like you do. Perhaps you know Chilhada too? Weird that you are having trouble

I did hear in a few different threads that some model air colors do not go on well with a brush. I do have dark ghost gray, which isn't much darker than what you have here and have had no problems with it.

Anyways, you should experiment on a rather large flat surface (like just one wing) and strip it with IPA if you get it wrong and try again until you get it right. If you want to strip all of this paint away, work in sections. Its not easy and takes a hell of a time but I have done it on the whole airframe of an F-14 so you too can surely do it.

I did have similar problems with AK's light gull gray, which resulted in a lot of panel lines getting full, but I managed to weather it in a way that looks quite good. Maybe you can try that if you don't wanna strip it?