Those X-Wings were meant to be flown by pilots still in training. Usually thrown in against TIEs. Just so they know what to do when facing superior craft (not that the rebels can get any). Therefore it's weapons are no match for a TIE and it's also not as agile for the same reasons. The shields are there to keep the recruit safe from accidents, because it also would have beenthe first ship flown by any recruit, hence a greater risk of accidents. Though still highly unlikely to happen, due to Imperial Simulator Training, but off course that will never be the real thing.
Another use for them was as a quick transport mostly used by specialists. Say that Thrawn's presence would be required at Coruscant, he would not have to pull his ISD out of combat, but could simply use an X-Wing. This however is now being done by the much more advanced TIEs, such as the TIE Advanced and the TIE Defender. Apart from that, the Assault Gunboat and the Missile Boat were also greatly superior to the X-Wing. However it was equipped with a hyperdrive for this reason.
As such the X-Wing was never intended to be used for any real combat. And it's poor performance in the combat is demonstrated by the rebels. Off course, Imperial pilots would have been able to get much better results out of this ship.