First of all, its NOiZE who is mantaining xta right now.
altough not all changes made it last release.. he may be short on time.
1) Arm Spider; this is the most unbalanced unit in XTA. A single arm spider and 1 L1 missle kbot (thats about 400 metal and 5000 buildtime) can defeat almost any unit, land or air of up to roughly 10x the value! spiders can hit and paralyse air (so normal units can hit them), and bypass any defence with paralysis. they build fast and cost 400 metal. there is no counter for spiders, as defences, powerful units and gunships are all targetable
Hm, i couldnt say they are greatly overpowered. Maybe a bit, but spiders are ezpensive in energy, and, dont do damage at all. So if you have only spiders, you cant kill anything actually.
If you have too few attacking units, spiders will be taken down, by other defenses units your enemy may have.
Have yet to see them abused in game.
2) The can: If you build cans in XTA, your opponent is likely to laugh at you, cans are terribly underbalanced (cost/power) atm. The Can can be defeated by A zeus or pyro (both half the price) or 4-5 l1 kbots (3/5 price), is terribly slow, has only 400 range and 5000 HP (for 700 metal, which isnt that good)
I would say, a can can kill a zeus and not die, same with pyros, so you are mistaken.
Cans take huge damage, and will help you penetrate defenses.
Actually, some guys complained its OP..
Mix cans with ranged units, and you will be able to sand the damage, wile ranged units take down structures.
3) l1 and l2 Bombers: never have any use at all, because gunships are so much better at any role, and are cheaper.
You are totally mistaken there.
Build 15 lvl2 bombers and you can kill almost any target. (antinuke, nuke, fusion etc), in one run.
You actually need lots of fighters (more than 20) to stop a good bombing raid.
On lvl1 bombers.. the cost is quite similar to gunships.
bomber
Gunship
Bombers are faster, speed is 9 compared to gunships only 5.56.
I feel them undepowered too.. but its matter of the use actually..
lvl 1 bombers are intended to hit targets as metal extractors and windmills, and last like 2 passes.. that is 2 metal extractors.
Ive seen lvl1 bombers used effectively this way... but its clear guships have more punch.
If you mass lvl1 gunships you can take out gollies...
lvl1 bombers wont be able to do that, in similar numbers.
More testing is required to decide...
4)torpedo bombers: too fragile (for cost), and not as effective as gunships.
I risk to say.. 5 topedo bombers can wipe out 1 millenium. not tested.
in other words, torpedo bombers inflict a huge damage.
Slow, though, not as easy to use as torpedo gunships.
5)L1 units: at the moment, the missle kbot (jethro or crasher) is so much better than the other kbots (cost/power) due to its long range and good speed. microed missle kbots consist of most the military power in XTA. the missles should be about half as damaging to ensure other kbots have a use; a standoff l1 harassment not a deadly long range threat.
Try some rockos against jethros, rockos are faster, and have more pucnh and hp.
Above all, mix unit types.
Ive tested, with success, NOT using misile kbots at all, in this version, with the last nerf to missiles. You manage to counter well.
6)Reaper; is not as good as the bulldog. this is insanity, because core are meant to be slow/heavy. since core lack a Panther (effective vs all N cheap) tank, they should have superior normal battle tanks, ie: reaper.
Dunno exactly what you mean, reaper is just as good as a bulldog, .. just one shot weaker iirc.
Also, as arm has the panther, core has leveler. 1 leveler > 1 Hlt.
7) mines cost towards unit limit, this shouldnt be the case as in small games (small unit limit) you cant use mines + have a big army 
not the case usually, ... maybe this has issues.. but do not show usually, as nobody uses huge minefields, and huge minefields are unefective.
microed ZIppers own all. I dont think zipper rushes are much fun for anyone, and I just dont see the point of a ZIpper unit. it just isnt fun to fight, and it is in itself encouraging a tactic most players despise.
Build llts.
The master counter against zipper rush, is to rush 3 jethros and 1 radar.
9) morty: cost/power/use, is terrible. a long range unit needs a long range (more than a hlt), and it should have range to match the dominator (although its still low dps and innacurate)
Hm.. morty.. seems not of much use.
Although.. its unmatched strategical core unit, the only mobile artyllery able to use high trajectory, and be accurate.
Its true is hard to use mortys, ... but just cheked, the cost is almost the half of domintars, in metal and BT.. so it may worth a try as rushing unit, well microed.
