In the odd game where players make mid cost unit spam (mainly skirmishers) magpie deal just enough damage to 1 or maybe 2shot them and can make cost very quickly.
However in teams all welcome players rarely make skirmishers. It's usually a few if any raiders at all into either expensive assaults (like minotaur) or riots, which are beefier than skirms and typically require more shots. Magpies perform significantly worse vs those.
Any large amount of spam that suddently appears in a specific part of the map can deal a good amount of damage. Some players make enough magpies to fly by and instantly kill cyclops and krows.
That's all the positive side I can see so far.
The negative side is that due to certain players essentially plopping gunships and rushing revenants every game, both sides constantly have a lot of AA immediately. That gives any air a short window to be very effective and operate mostly unchecked. After that, you need either likho (fast and moderate HP) or krow (slow but very tanky) to be able to dive over the front and pick off enemy units. Anything else gets instantly vaporized.
The most attentive players can find good targets with a mid size flock of phoenix for a good part of the game.
The few players that mass tons and tons of magpies are usually super passive, like almost asleep at the keyboard. Then they take their GIANT flock and hit one point of the map, which has AA but rarely enough to handle 30+ magpies jumping out of nowhere. If you're controlling the magpies you might think you're doing good, but what is actually happening is your fleet woth thousands in metal was just hovering the base doing nothing while the team was already winning, and then you flew in to deal a killing blow on an already weakened position.
If that metal was spent supporting a part of the front earlier, the match would have been far easier for your allies.
How many times have we seen the magpie spammers get called to respond to a single odin flying towards a singu and just watch that odin reach its target?
Magpie spam is just one more strategy to add to the pile of things that work because my team was already winning.
If TAW was not so conditioned to getting AA so early every game because of gunships and if players in general were more aggressive and reliant on small cost units (like 1v1 matches typically go) magpies would have a longer effective lifespan and a wider pool of targets.