With regard to the discussion of DESTROY GUNDAM, that's all from Gundam SEED Destiny, which is widely regarded as one of the most **** Gundam shows. Of course the Destroy Gundam is a cheap knock-off of the Psyco Gundam (from Zeta Gundam, of which SEED Destiny is a cheap knock-off), which was notoriously difficult to control and wasn't ever mass produced because of that.
As for why they had other mechs than the destroy gundam, it's just that destroy gundam was developed more recently, so they still had an organized force of gundam-sized huge mechs. The villains in this part are a combination of super-racists and the military industrial complex. they are more concerned with being evil than any kind of real efficiency.
I am also in agreement with Legend of the Galactic Heroes being the pinnacle of anime. I eagerly await the day something approaches its greatness.
@Luis i can safely say that Legend of the Galactic Heroes has essentially no teen fanservice, unless you like cute space fleet commanding young men.