I don't think I have any insight that you lack, but if you read what you have written here, I think you'll agree that e answer is pretty clear. You don't like the CX bike and don't feel safe on it. You don't ride much off-road anyway and are just as happy on the road in the mountains as you are on the trails. When you go on the trails on the CXbike you don't really enjoy it because you feel beat up.

All in all, there doesn't't seem to be much sense in keeping the CX bike. Whether you trade it in for the used soloist, or for a different bike (maybe a CX bike that you actually like, to retain the versatility?) is another matter. That depends on how much you like the offer on the soloist.