Uh, are you on crack, Vonta? Sorry, I try to hold the insults in, but when you say things like that, I just have to ask. How can 20 ships, which thus have about 60 worthwhile weapon emplacements, do as much damage as a VSD, which has 130? Sorry? No, I didn't think you had an answer.
How the hell would one little bloody thermal detonator dropper on each ship account for more damage than a 900 meter ship can deal out? Give me a break, here. 1228 meters worth of ships is what we're talking about.
a) You're not taking into account that the values you're talking about are three-dimensional. Bearing in mind that a shipyard would probably be at least 10,000 meters wide as well as 40,000 long and maybe 10,000 deep, one can safely assume the volume of a shipyard is 4,000,000,000,000 cubed meters. Assuming that the thermal detonators deal out damage, as you suggest, on a flat plane, 25,600 meters seems like something of a scratch, doesn't it? Actually, hell, let's assume the damage stretches ten meters high. At the most, you've done 256,000 cubed meters of damage. For those keeping track, you'd have to do that about 15,625,000 times to destroy one shipyard. Not that they're solid steel, but I think you get the point.
That's also assuming they somehow all just dropped 64 thermal detonators apiece and all of them hit their targets and all of them scored hits (which would also suggest to me they have no more damage to do), which of course is crap.
But, yeah, if you want to say that you've done negligable damage to one shipyard and are now spend, as your math (glorious math) would seem to suggest, I agree.
b) You're not taking into account that while thermal detonators, according to what I've just read on the CUSWE, are supposed to obliterate everything in their blast radius, they're also used normally as weapons on the ground. When you're dealing with industrial-class durasteel, one might assume that SLIGHTLY less damage gets done. You know, how a laser cannon can blow up a speeder but can't do @#%$ to an ISD?
c) You don't seem to understand that a single turbolaser blast can do massive damage. Observe a tubolaser blowing apart buildings in one shot. Observe a turbolaser leaving massive craters.