on a per man basis the defensive secondary and particularly corners are more important than the oline.
while lt requires a rare kind of athlete, a slight deficit in lt play will cause some trouble (like gandy, or even the not so great lt on pitts) for the o. a slight deficit in corner play will result in break away touchdowns.
there's a reason why no on will pay that much for even the best C, but will pay it for even just good but not great corners (near pro bowl/pro bowl corners get 10 a year, good ones get 6-9).
that's the way it is bill, all nfl gms are big on spending high picks on secondary, that's how it's done.