Interesting.

I would liek to take the idea a little further.

Have it so that as the armor takes damage it begins to allow mroe damage through to the point where small weapons have the original effect. So at first the armor will need the big ships to widdle the armor away to an extent by using missles/rockets and by the time they are out the smaller ships could finish the job against the cap ships.

Ships like the Ragnarok and the Behemoth would still take damage from small weapons but would take it at a lowered rate nut slowly the enemy would be doing more and more damage to the point of the weapons intended values.