I always glass the center wing join of all of my ARFs, too. This would help keep the wing from breaking in half on hard landings. Especially, when you have 2 aeleron servos and/or retracts, the wings are more prone to breaking in half. When I first learn to fly, the wings on my trainner keep comming apart on hard landings, I'd learned to glass center wing join of all of my ARFs, both sides, and never have any problem with the wings again. I have instant where the fuselage broke in half on landing but the wings are still in tack. I think it is worth the time to glass the wing center.

About the force acting on the wing. You bet that there are a lot of forces trying to break the wing apart, especially, on rolls and recover from steep dives.