a couple points here:
1. regarding the drack, it was my understanding that the drack fought in the earlier shadow war (that was why they knew minbari, when they were fist encountered), just everyone had forgotten about them.
2. regarding vorlon fighters, i don't have much expierence with them but my opinionj is that they are actually a prety decent fighter. Their AF weapon helps make up for their lack of a good dogfight score, and with the beam trait they are decent for clearing out smaller hips taht aren't worth the attention of the larger ships.
as for more ships as a whole, I'd say there are 2 basic schools of thought on this:
1. as anchents the vorlons and shadows have been around long enough to know what works and what doesn't and they'd only use the best designes they'd come up with in their munti-thousand year existances. Thus they should have only a handfull of designes, each with the abilikty to fill multiple roles in a fleet.
2. because they've been around so long they hould have collected a good many varietys of ships, each speciallised to fill a single role to the best of it's ability.
personally i think the second philosophy best fits the vorlons as the force of order, whereas the shadows, believeing in growth through conflict would tend to have fewer more versitile designes.
so, yes on more vorlon ships, no on more shadow ships (except posibly variation within the same spider-crab designe).