I remember the overshield not being an extended shield, but also strengthed as well. In halo Infinite, that shield would pop in like a few extra shots or by one grenade. It felt more like a get-out-of-jail card, and less as a strategic objective holder or sieger.
Overall im saying, is that its just getting popped too fast and i remember it being much stronger.
I think one issue with making it stronger is the fact it is more versatile than ever as you can hold onto it and use it at an opportune time. If it activates too quickly and is too powerful, it will make it too overpowered.
Overshield always felt very powerful in Halo 3 because you got invincibility frames when you picked it up.