AGN Attacking Leningrad?

Hey guys. What are your opinions on Army Group North attacking instead of sieging Leningrad. Would AGN win? Would it even be worth it? Fully securing Leningrad would have freed up all of those German troops; they could have been reassigned to AGC or AGS and help fight off Operation Mars and the Battle of Kursk. Also the soviets couldn’t have a counter-offensive like they did at Stalingrad. Right?