don't confuse efficiency with 'cheap'
In the movies xwings go down in all of a single hit more than tie fighters, their shields are effective vs glancing blows but not solid hits (of course xwing and tie fighter drastically upscaled the number of hits a player ship could take but that was a game mechanic) The empire needed to deploy tie fighters to millions of worlds and millions of ships and stations, you are comparing mass produced fighters for an entire galaxies military to highly illegal production of vessels for an insurgency group and groups wealthy enough to bribe local officials.
A tie fighters role when stationed was to engage civilian and merchant craft that were running blockades or patrol lines and provide fighter escort for bombers and gunboats, they didn't have to be all that heavily armoured because most merchant ships were unarmed (imperial policy to confiscate anything that could be a threat, remember Han's quad turrets were VERY illegal and it took two force sensitives, and one of the best pilots in the galaxy to fend off three tie fighters...) if tie fighters were insufficient then blastboats or patrol cruisers would rapidly enter the scene.
In deployment operations, star destroyers and other heavy vessels would use tie fighters as force projection by leaving a squadron in an area to to perform its mission (escort, support, patrol, search etc) while the capital ship went to the next system needing its attention, recovering the squadron later. For planetary invasion and subjugation Ties would be expected to provide air cover after bombardment (either orbital or from bombers) and eliminate planetary defense fighters (illegally modified, probably very poorly crewed and mostly old) and do strafing runs on soft targets once anti aircraft batteries were pounded to oblivion.
In all these roles you do not need a heavily shielded, hyperspace capable, expendable munitions armed, multipurpose fighter, you need something very fast, manuverable, hard to hit and with big guns (which ties had for their size) you would have a limited number of blastboats, gunships and bombers that would be specialized and vastly more effective than a multi role fighter and much more efficient at projecting your firepower and capabilities surgically.
The rebellion on the other hand needs to preserve the ships it has from losses and REPAIRS and pilot injury (shields provide this)because they have very limited resources to replace costly fighters, repair costly fighters with costly highly illegal smuggled parts from undergound manufacturers and get good recruits that would stay alive long enough to rival an imperial academy recruit. They need to have expendable munitions (torpedos) to attack targets of oppertunity when using a larger vessel is utterly suicide or would take a very limited heavy hitter off another job. They need to be able to work outside of a mother vessel and hide easily (a hyperdrive allows the mobility to shift bases and perform independant missions)
the empire could afford thousands of trillions of tie fighters if it needed to (they built two deaths stars as a 'budget oversight' hidden in a single spending bill that wasn't worth the senate's time to review), the rebel alliance couldn't afford to lose a single one of its tens of thousands of ships. So in effect you could claim that the empire not only fielded a more efficient fighter for the cost and mission, but also was vastly more fiscally responsible than I think almost ANYONE gives them credit for. when stacked up against more effective fighters the tie seems lacking, but that's only because it was a better tool for the assigned mission (besides even with the 25K ISD fleet complement alone the empire had 1.6 million ties, 300k tie bombers, 50K skipray blastboats and 125k assault gunboats available and that's not counting a sngle other vessel in the sector group or any other station or planetary garrisoned forces and none of the reserve or augmented sector/fleet forces) and I have to believe that an ISD that is deploying a garrison to a planet is ferrying the fighter complement as well so it would have well over 300 fighters on board (with 72 assigned to its own air wing) which would bring ties to most every population center over 1 million people.
