actually quite the opposite:

coupes and sedans are built off the same chassis, use the same wheelbase and use the same drivetrain/engine...it also uses the same amount of sheetmetal

the real kicker is a coupe has a much larger door (compared to 2 smaller doors with a support brace between) making a much bigger hole in the side which reduces structural rigidity so mfgrs reinforce that larger hole with more steel making the coupe actually as or even heavier than the normal 4 door models

bmw used to race m3 sedans over the m3 coupes for this reason alone...there was no stigma b/c it was 4 doors and not as cool...in fact real time racing was happy to get the TSX for its better ability to race at the limit over the the RSX (various reasons were also key such as engine / suspension / drivetrain) b/c it didn't flex as much as the rsx did b/c it was a coupe/hatchback and the tsx was a much stronger frame b/c it was a 4 door