I am just starting to get tired of all the "Unit X is OP and unit Y is UP" threads.
First of all, when you go for a unit that is not the only unit you get, you get a "set of units" that comes with your factory. Local imbalances are fine, it adds to the game. If you are really good playing with skirmishers you should be able to pick the factory with the best skirmisher to really exploit that OR pick the factory with the worst ones since your skills would bring them up to par with the other ones and thus giving you better units in roles you are not as good with. A unit is not OP because it kills all the other factories equivalents in a straight up 1v1 fight. A unit should ONLY and I mean ONLY be considered OP if the game degrades to building that unit. In other words when the building of that unit is the only valid strategy you can go with because if you do not, your opponent will. If you think a unit is in needs a nerf prove it by degrade the game unto that unit, that way the developers HAVE to nerf it in order to keep the game balanced and varied.
A unit is not over powered because you have a hard time countering it. If there is a unit you frequently lose to, copy that players strategy and use it yourself. Either his strategy is better then your and in that case you should use it instead of your strategy, why should you not play the game in a way that makes you win? What is more likely to happen is that you will come across a player that knows how to play against whatever it is you are doing and then you can learn from him, find out how to counter it and then go back to your original strategy.
Under powered units are a bit harder. A unit is not underpowered because it is the worst in its category compared to its counterparts. Remember, you do not buy a single unit, you buy a set of units when you build a factory so if its other units are stronger then their counterparts then it is fine. A better question is "What factory do players not play with?" and then ask yourself "Why are people not playing with this factory?" It may be because it is a situational factory, it is only a valid pick on certain maps. Is the naval factory under powered because no one builds them on land maps? No, it is because a naval factory is not good factory for that type of map. Is the spider factory under powered because you never see it on Red comet? No, because spiders are not meant for big, open maps, they are meant for hilly maps with lots of cliffs where they can really exploit their wall-climbing advantage.
A factory is under powered when it is never built, no matter what map or situation you are in. Now we can start working on bringing it up to pair with the other factories by improving its units. When doing this, I suggest a ridiculous big boost. A small boost wont help since people are already in the mindset that this factory wont work so they wont even try it. It is better to make the factory over powered instead so players start to use it and then slightly nerf it back down once it is back in the game.
Cheers! -Emblis