The automation isn't there yet. The LCS class, among others, was designed with heavy automation for reduced crew size (as crew costs are the largest component o

The automation isn't there yet. The LCS class, among others, was designed with heavy automation for reduced crew size (as crew costs are the largest component of a ship's costs over its lifetime), but it turns out that they simple carry too few people to do all the maintenance required. In addition, there's also been concerns with damage control capabilities with smaller crew sizes. As to your second question, larger ships simply have better economies of scale. Larger generators, more missiles, bigger radars, etc. If you could quantify capability, larger ships have more capability points per dollar. (On the other hand, you sometimes don't need all that capability, and there's always more missions to be done, so a cheaper ship can be more cost effective even if it's less efficient.)