I actually quite like this idea. Keep in mind a sufficiently large bubble shield will also be stopping missiles before they reach your ship, even if its own shields are down and the force fields are taking damage directly. They'd also catch warhead torpedoes.
I planned to build a defensive cruiser for employment in formations that would cover for the fleet using this. Incoming fire from the enemy's first salvo hits the cruisers forcefield. The ship itself isn't damaged, because the forcefield is a docked entity. It doesn't necessarily need to have strong shields backing it up either. But after employing it to catch that first salvo, and maybe subsequent missiles, drop it so your own direct fire can get through.
I think just using it to catch that first alpha salvo is a very interesting idea (and perhaps later salvos from the enemy's main weapon). You can turn it on and off, and just sacrifice the forcefields, and stop your own firing for a short period.
The trade-off is dodging a (hopefully) significant part of incoming damage, while only having a small effect on your damage output...
I think anyone not considering the forcefield to actually be part of their ship is demonstrating some interesting aspects of the way humans think though
Whether its forcefield or armour, and whether or not it's separated from the rest of your ship by an "air gap", it's still part of your ship being destroyed.