Adding to stats, in the batch of games I analyzed there are 38 games with average rating of 1500+ and 297 games of rating 1000+. Beetles were built in 0 out of these 297 games.
Now following the info I got in the balance guideline thread (in that a usage statistic is not enough in itself to prove that a unit is UP), I'll make a comprehensive argument on why beetles are underused. The gist of my argument is that beetles are an extremely situational unit that has better alternatives outside of a very narrow range of situations, and even in those Cybrans have options that aren't much worse. Therefore, players don't bother learning the unit, since they're very rarely worse off not using it. To do that I'll analyse, one by one, every beetle use case I can think of, starting from least useful.
Outclassed by T1 artillery. 160 mass worth of cybran artillery deals the damage of a beetle in about a single volley, but will probably fire more. They also have more total health, can hit multiple targets and are harder to get rid of once they spread out. Beetles do require less space in transports compared to arty, but additional transport cost changes little.
Apart from extra speed, beetles are pretty bad for raiding. When raiding an undefended area that won't have defending units for some time, rhinos and medusas are superior - they can defend themselves, they don't have to be microed, can hit multiple targets, deal more overall DPS and you probably already have some built. One case where beetles are okay is raiding an area with an important target that's both exposed and can quickly respond, e.g. T2 pgens in an exposed base after a player's death in a teamgame. I've seen one such play. This is IMO restricted by the fact that you have to predict a raid opportunity in advance to build units dedicated for it.
This applies to at most T2 firebases, as beetles are outclassed by T3 (more below). Obviously medusas are better at killing T1 PDs. They're also more effective against T2 PD firebases since they have way more overall health, can spread out, don't have to get very close to deal damage and need less micro. More health is especially important, as advancing units will lose the same amount of health before they start dealing damage, which translates to more mass lost for beetles.
I'll list issues with beetles vs. land in general first.
- Unmicroed beetles explode the moment their target gets in range, so their AoE is wasted. You need to micro them to get them to explode up close.
- Unmicroed beetles told to attack a target don't follow it, instead they head to its last location, stop, then move again towards it. This usually makes them die before they even reach their target if it's retreating.
- Attack-moving beetles doesn't make them pick a target. You have to ground fire or pick a target manually.
All of this was tested ingame.
I don't know if last two points can be fixed. They weren't until now, I assume it's an oversight. The first point AFAIK is easy to fix.
From my experience, beetles are outclassed by T3 armies completely, just like T2 tanks. Without a deceiver, T3 units have enough vision and range to kill advancing beetles easily. With a deceiver, T3 units just have to kill an advancing deceiver first, which doesn't give beetles much more time. Either way, beetles have to hit multiple T3 units to be cost-effective, which means beetle micro. Compared to gain (a handful of wounded / killed T3 units) it's a waste of attention.
Beetles can be cost-effective against T1 spam (with a lot of micro), since they one-shot every unit, have a sizeable AoE and enough health to reach enemy units. However, when fighting T1 with T2, you don't just want to kill enemies cost-effectively, you want to get a critical mass of T2 units. A mass of T2 units can fight T1 at a better cost ratio than (at best) 1.5 you can get from microed beetles.
Anti-ACU, transport drop
From my experience, transport drops became extremely situational, I had a single teamgame on Syrtis where I managed to kill a retreating, barely alive ACU by dropping a few beetles on him. That required an enemy ACU to be barely alive, his teammate not to provide air cover, me to quickly build beetles from a T2 factory and a bit of luck with the transport drop. Outside of very specific situations beetle dropping is dead. Of course, you can still score a kill on an unattentive Setons back slot player, but now you need 20+ beetles to pull it off.
Anti-ACU, on land
Offensive ACU snipes with beetles (on land) are dead, unless it's a really isolated, low health ACU. I tried it several times myself. If the ACU has any land support, almost none of the beetles will survive. If it has no land support, you still need a lot of beetles to kill a healthy ACU and many of them will die without damaging it. In general, putting the same mass into a T2 army (to kill the enemy army then surround the ACU) or an air snipe is better.
Defensive snipes (to stop an advancing ACU) are hard to judge for me. I suppose that, if the enemy ACU is advancing in front of an army, then sending beetles to hurt it for 1k damage each is better than sending T2 tanks. On the other hand, there's risk involved:
- Beetles can't secure map control and (I conjectured) die to T2 armies, especially to an ACU with omni. Small numbers of beetles won't stop an ACU and most will die to overcharge, large numbers are made at a cost of not making an army. If you build a ton of them as a gambit, then your opponent has an army and you don't, so he can just secure map control and not push.
- Outside of the above gambit, corsairs or T2 gunships seem to be a better alternative in this scenario. Unlike beetles, they're guaranteed at least one pass and can make multiple passes. They're also targetable by flak and interceptors rather than ACU overcharge and a land army.
I didn't test this ingame, but I understand that beetles are good against some T2 units. Apparently they're good against hoplites/mongoose when microed. I believe they lose to regular T2 armies since multiple beetles require a bunch of micro, plus an army can kill them before they get close, even with an accompanying deceiver. I have no idea how useful mass beetle spam would be (e.g. to bait an army into attacking). I'm pretty sure that making many beetles instead of T2 tanks to bait an enemy army trades away map control.
To sum up, beetles as they are now seem to be a unit with very niche uses. They're great against mongoose and hoplites, they are okay for raids in very specific situations and can stop an advancing ACU in very specific situations. Everywhere else they're outclassed by other units. Now, first and third case are reactionary - you make beetles to counter a specific strategy, or you make them because an ACU is coming and you have no better options. The second case is very situational - you have a window of opportunity sometimes, then that window is gone.
In other words, beetles are only worth building as a reaction to a few specific situations and enemy strategies and outside of T2 stage barely have a good use. Anything that's your initiative - killing eco, drops, raiding, capturing a position, ACU snipes - is better served with other units. If you do have some leftover beetles, they do a poor job in all these things.
I'll leave the suggestion how to fix them for another post, this is enough of a wall of text.