First, I am surprised that such supposedly decent speakers do not like being crossed at 70Hz. Try 80Hz@24dB crossover. Also check that you have not accidentally switched polarity of one of the speakers. If you still have problems, it's a problem with the amplifier or something else IMHO.
Next thing, have you sound proofed your door? It'd recommended to completely seal the middle section of the door and also apply a few tiles on the exterior door skin. (I have a layer of Dynamat Xtreme and a layer of Dynamat Dynaliner on top on my front doors, and a layer of RAAMmat BXT2 with a layer of Ensoline in my rear doors). This should considerably improve the bass response of your speakers.
Finally, as others have pointed out, it's normal to feel like the speakers closest to you hit harder. The problem is that the human brain always perceives that the source of the sound is based on the direction from where the sound reaches your ears first. In cars, left speakers are at least a foot closer to you than the right speaker and so you always perceive that sounds that are meant to be centered come from the left speaker. The way to fix this is to buy the head unit or processor with time alignment. It makes a noteciable difference IMO. I use a kenwood x994 with custom TA setting.