Until more recent versions, when its sprite was updated, Falcon did not have two small energy mounts ahead of the medium turrets. It really was a destroyer posing as a cruiser, little more than a poor-man's Medusa. Old Falcon had no PD unless it used its medium mounts for that purpose, but then it had terrible firepower comparable to a frigate. Overall, old Falcon was rubbish, much like Hammerhead. Today, standard Falcon is good. It is just slightly better than what you can get from a best-in-class destroyer, but definitely less than what you get from most cruisers. It straddles the two classes, and it is effective for what you pay for.
Bear in mind that the Falcon paying Cruiser costs also gets Cruiser benefits, most importantly from ITU/DTC.
...and cruiser downsides, such as less speed from Augmented Engines (at least as important as shot range) and higher OP costs for hullmods. Old Falcon had puny OP for its size, and had trouble affording everything it needed. Its stats would be great if it was a destroyer. Current Falcon has a bit more OP (for its two new small mounts). While it still does not have plentiful OP, it has enough to make do.
For the Falcon, cruiser-size was a net-loss. Extra range from ITU/DTC is not enough to make up for the downsides bigger ships get.
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As for OP, the only high-tech capital that matters today is Paragon. The others just get in the way of buying a Paragon. Maybe 0.8 will make the others more useful? For low-tech, they do not need anymore battleships because Onslaught is so brutally effective. Maybe if Onslaught's costs get raised to (nearly) match Paragon, then a cheap low-tech battlecruiser may make sense, maybe a slightly bigger Dominator with better angle coverage. Midline is in trouble, though. Conquest is no battleship that can match Onslaught or Paragon. I would like to see something like a super Eagle for a midline battleship, or maybe capital-sized Eagle and Heron combo.
Similarly, there is only one high-tech destroyer combat ship, Medusa, although it is so good that high-tech does not really need another brawler. (I consider phase ships its own epoch not the same as high-tech; they feel like a mod faction in the game.) High-tech does not have hybrids or carriers of destroyer size though. Then again, since energy weapons are usually completely inferior to ballistics, that having more ships may be pointless if they have junk weapons and stuff like current Aurora.