How about 1 moderately agile torpedo boat vs 1.1 phaser hedgehog though? Because your comparison is ludicrous. On engine costs alone, it'd be 1.5 but that's far from the only cost. The letter grades are relative affordability for their ship class and role, they're not going to let you pump twice or even 150% as many ships.
Packing on phasers for coverage has costs. We're going to spend as much on weapons but get weaker firepower in our firing arc and less punching power, which has been quite relevant in past wars when using 2nd rate ships against 1st rate ones.