Some warships are intended to be faster, others are intended to be slow. It just happens that we had two mid-level warships that are slow (Stralsund, Agamemnon) and the fast warships (Defiant, hybrid Myrmidons) were high level, and one of the slow warships (Deliverance) was gaining speed from a bug. Now we've also got a mid-level warship that's fast (the Athena). Higher end SOLs are supposed to be fast, but at an extreme cost in acceleration.