Not a silly question at all, that sounds like unintended behavior. The .psd files should have a similar lightness to the .png files of the exported textures, so yeah, I'd try messing with adjustments until you can get similar results.
I wonder if the color differences might be your image editing software encountering some kind of version or setting mismatch with the .psd files- I haven't been able to test them myself in photoshop, but when i open them in krita it displays similar overall lightness to the exported .pngs.
I'm glad you've been finding the file layout easy to work with, I hope you can get the results you're going for!
It must be a software thing then. That's bizarre! I've attached a comparison between Krita (left) and Clip Studio Paint (right) and it's literally night and day. Both versions (IronRust & Firefade) are the exact files are from the most recent update. I don't think there's anything you can do on your end, since the files aren't broken, it's just CSP I guess? Wild. 