hmm they wanna weaken the siege tanks in siege mode only ? then better dont siege the tank, in siege mode, if the damage is 35/50 (light/heavy), but it takes 3 seconds to fire a shot, compare to unsieged mode, which is 15/25, but its 1 second per shot, thats 3x more shots, so dpa wise its alot better.

Ya have to take consideration of the area damage and range, but the area damage most likely are doing against your own units if against close range units like zealots, zerglings, or those bugs after u kill off some zerg buildings.

so the benefits of siege = better range(if enemy is far), area damage(if they are packed together, better against high armor units
and the benefits of not siege = higher dpa, can move(can survive longer), wont damage own units, doesnt block traffic(they can move =P)

would be nice if they introduce some kind of armor/bullet upgrade for siege tank that wont/reduce the area damage to own unit/building for balance. else siege mode i think have less advantage(it should have more).