I am new to Mid-power myself, however I have been building all my model kits with Epoxy from day one.
Micro Balloons and milled fiber are not to make the epoxy lighter ( although that may be a sideline benefit ) but those substances mixed in with epoxy can increase the strength of the bond by up to 300%
It also has the added benefit of thickening the epoxy so it is easier to shape for making fillets.
I have not used JB wield, I am using the standard hobby Shop epoxy and adding milled fiber as needed or to thicken and strengthen it for certain joints.
With a little care you will find that while epoxy can be annoying, it is in some odd ways easier to use than other glues.
You can determine its properties yourself, use 5 min or 12 min or 30 min ( warning, 30 min only starts to set up in 30 min, it does not cure fully for several hours ) I build Estes models with 5 min epoxy, that gives me enough time to carefully place a part, while never having to hold it in place longer than 5 min and ends up with a bond stronger than CA.
On Mid power models I am sticking with 12 and 30 min Epoxy, but I am using milled fiber as an additive. You can determine how thick and strong it is with milled fiber or micro balloons.
Personally I have come to like the way I can control epoxy so much that it is the only glue I use even on the small models.