a honda that out handles the wrx? It's possible certainly. Handling is mostly governed by tire grip, weight (including distribution), and geometry. Exit and entry speed are more complicated questions that effect racing as opposed to just handling and have a lot to do with the total car. If a car has better grip and less weight than you with a decent geometry, yes it will handle better. Is that what you're asking? That's just simple physics.
As for the WRX understeering, that's very true. The stock WRX drives more like a FWD car than a RWD car. More understeer than your civic? I'd doubt that, but that's not your question. WRX's are easily modified and improved. Understeer can specifically be addressed with a fatter rear swaybar and a pair of rear endlinks. If you want to make your car oversteer, you can too. It's just not going to make it any faster.
WRX's have different advantages and disadvantages against a civic. Comparing the two would be fairly in depth and I don't have the energy. You're very vague in what you're asking here. Can a WRX be faster than a civic? Sure. Stock for stock it already is through almost all tests. Can it be modified to handle a modified civic? Well, that's just a question of which mods are on each and really impossible to answer vaguely.
Can a WRX "hang" with an sti and an evo? Sure. Are we talking stock evos and STis? For not a large sum of money, you could beat either car in almost any test of capability. The suspension in particular of both cars is easily beatable with tires, swaybars, and coilovers. In terms of power, a turbo swap would out class either stock offering.
2015 STi: Still Stock
04 STi, 04 WRX: SOLD