I agree that cabin space in the PA28s is cramped, but you're comparing
big 6 cylinder aircraft with 200 hp or less 4 cylinder aircraft except
for the 235/dakota series, which combines a cramped cabin with a big
engine and can lift small elephants if you can get them into the cabin
:-)

The Arrow in particular gets fine performance from its 180/200 hp
engine (1000 lb useful load), though the Mooney is even more efficient.