See Attack Effects for a more practical, shorter, equipment-based description of attack effects and the units who use them. This page explans what the game intended, even if it didn't achieve it, and gives stat tables.
Anti-air units are weaker than anti-ground units to make up for being effective against weaker flying units. They have a distinct lack of capability to defend themselves, but are treated with higher attack power. They also have a great mobility to catch up to air units and protect themselves within terrain. The exception to this is obviously the praying mantis, who never gains more movement in its equipment and stays at the slowest movement besides the pillbug, and both the mantis and cicada on the player team in respects to the fact that their weapons must level with their allies.
CNTPEDE"Anti-air gun unit" tread, mov 5. macc 100. Gun-'versatile' tread unit. guns become anti-air, stats exceed normal balance. weapons: various centipede fangs various effects, side cannons high attack power
Both anti-ground units are completely different, with dragonflies being overly identified as a flying unit with high mobility and low defenses, and the moth being overly identified with ground units to deliver the minimum of mobility but high defenses and attack abilities. Obviously, this makes the dragonfly a very weak drone in the long-run, as it has the lowest HP besides the firefly, no extra defense, and only 20 more speed, with no extra beam effect. Dragonflies can, however, equip any melee-rank melee equipment, meaning +15 defense than other flying units.
See Attack Effects#Beam for the role of beam element across the game. The primary beam drone is the firefly, and is intended as the only beam drone in the game, with the exception of the Blast Guns and with the Badlands not being considered canon to the Story Mode and its own unique battle experience. Beam is the most powerful effect, and saps the firefly greatly of defenses. Her beam weapons come later than other cannons as well.
The Badlands changes the foundation of battle greatly, eventually giving all enemies beam weapons as normal and attack boosters. These drones gain beam element at different times, but the only ones who do not have better weapons than their beam weapons are the butterfly and moth in the early Badlands (possibly even before the endgame or during the story portion of it.), and then the pillbug, bee, and in the second last level, the centipede.
These first 3 drones gain their beam element weapon in the middle of the Badlands, where their true final weapon is actually non-beam element. These drones excel with the beam weapons, making it a choice between no added effects and beam element. The centipede and scorpion's final guns are beam element, but the scorpion never joins the player (that would be too cheap, obviously), and the centipede gains the beam cannon two stages before the final stage in the Badlands.