Jesters fulfill a particular niche of a defensive and reliable T1 air unit. They can also be used for raiding but due to their low hp they are pretty easy to snipe and die to T1 MAA quickly, that is by design. You can't compare its DPS/mass cost to the bomber's because A) The DPS of a bomber is greatly exaggerated and no, when it's min 4 and you are dealing with some raids nobody is going to micro their bombers. B) Bombers tend to miss a lot (but they deal AoE so they are better vs armies). Basically, Jester is designed to be a defensive unit that kills single/small groups of units on your side of the map with its secondary purpose being sniping engies/raiding mexes. Bombers are better on the offensive (killing engies) and attacking armies.
Both units have different roles and are better at them than their counterparts.