So there are some reasons that are often touted as to why front loading has become more popular. The point you make about the riders weight being closer to the rear wheel but I think strictly speaking that one doesn’t actually hold up so well if you think about the direction your weight is moving relative to where the rear hub is. The other point you make is also true about a front load making handling feel slower but this is where it helps to choose a bike that has a ‘low trail’ geometry (like the AWOL) which goes some way to offset this. Ultimately though I think it just comes down to personal preference. When I ride loaded I like my bike to feel as much like it does to ride unloaded. For example I used to ride a surly cross check with the standard two outline rear panniers and riding out the saddle you really notice the ‘sway’ they cause at the rear end. My current strategy is not so much front loading but really having weight balanced between lots of places in the bike. So that means heavy items (tentpoles, pegs, knife and tools etc.) go in the frame bag and other stuff divided between saddlebag and front load with probably only slightly more weight in the front. Those latest bags will mostly be for a small cook kit on one side balanced by something like waterproof clothing and gloves on the other. TBH no one gets it perfect to begin with and every tour involves a bit of juggling stuff around and trying different things out. More important is that the frame really fits you well.
Saying that one of the best tips when using a bivvy set up that I got from Jesse Carlsson is just to leave everything in side of it. In Japan, my inflatable sleeping mat and ‘quilt’ just stayed inside the bivvy and got rolled with it and my groundsheet meaning at the end of the day I just threw it on the ground and got in.