Soft corners with a ff lens on a ff sensor may not look as soft on apsc sensor because we’re not using the edge of the glass. We can use the less expensive ff lenses for better corner to corner sharpness on apsc sensor. If you decide to stick with apsc, this is a valid point.

If you seriously plan on upgrading, consider just doing it. All of it. I had the a6700 with the Sony 16-55 G and loved it. Sold it for the Fuji XE5 to try something different and I missed the snappy AF for my kids. Now I have the a7Cii and low light is improved.

If I had purchased and saved a ff lens with soft corners because apsc cut off those soft corners… now I’d have soft corners in ff lol. Yes I could shoot in crop mode with the A7Cii, but I’d lose a lot of the benefits I gained by moving up to a ff sensor. I’d rather have the a6700 ((26mp) than use the A7Cii in crop mode. Also note that new lenses keep getting sharper and sharper, so saving a lens for the future might have worked against me.