Don't be too envious, the Sony 28-70 is not a good lens any way you slice it. I'm not only taking Klaus's opinion into account - incidentally our video operator rented one recently (to be used with A7S II), and she expressed rather... negative opinion of it's quality. And that was for video at 12MP.
I honestly don't understand going to FF, then being willing to compromise so much on image quality for the sake of compactness. If you value compactness above all else, there is MFT and a variety of APS mounts.
There is a good reason all the film kit zooms went the way of the dinosaur (with the Yucatan event for them happening about 15 years ago, in my book, right when APS-C DSLRs became good, affordable and widespread). I can understand getting the urge to try something left field - once I almost accepted a Canon 28-90 kit zoom as a gift - but you need to decide whether you want to get consistently good results without constant frustration.
I honestly don't understand going to FF, then being willing to compromise so much on image quality for the sake of compactness. If you value compactness above all else, there is MFT and a variety of APS mounts.
There is a good reason all the film kit zooms went the way of the dinosaur (with the Yucatan event for them happening about 15 years ago, in my book, right when APS-C DSLRs became good, affordable and widespread). I can understand getting the urge to try something left field - once I almost accepted a Canon 28-90 kit zoom as a gift - but you need to decide whether you want to get consistently good results without constant frustration.