yeah... the mechs COULD have been a bit more elaborate but the simplicity of the design was necessary in order to make it as agile and lifelike as it was supposed to be... u see, evangelions were in fact nearly humans in make up just that they were of a different form...... so they weren't really mech, just giants sapien-like beings with protective and controlling armour encased around them as was explained in the anime itself..... so u are right.. they aren't mechs....
