I find the mig paints to be fairly inconsistent too, or maybe they just need a more delicate application than my heavy handed approach will allow!
With Tamiya I find them too dark also but lighten with appropriate colours. I wouldn’t really use white for all colours though. Yellow, or yellow/green for green, buff or deck tan or khaki for brown, and white for greys or yellows, although there are infinite concoctions possible! And I find using some clear gloss added to tamiya colours really helps with getting a consistent colour which doesn’t change too much with all the other processes we like to go through. They are too Matt out of the bottle I think. Oh, and I also find lacquer thinner to really help with spraying tamiya, very much so. And so much more forgiving than all these new true acrylics…
I’m all for non toxic paints, but there is a price to pay, either way.