Two Meters of Concrete
The KV-2 had many advantages compared to analogous SPGs that were designed at factory #185 to fill the same niche. For one, the KV-2 was built on the chassis of the KV-1, which was already accepted for service, the only difference being in the turret and the gun. Factory #185 was designing vehicles on the SU-14 and T-100 chassis. The SU-14 was abandoned in 1938, and the future of the T-100 was under question. The KV-2 was also smaller than its competitors, and had thicker armour.
The KV-2 also had plenty of drawbacks from the point of view of the artillerymen. In order to fit the 152 mm M-10 howitzer into the KV-2's turret, it had to be shortened, reducing its already humble concrete piecing effects. The ability to penetrate 90 mm of armour from a kilometer away was not enough when dealing with bunkers like the Finnish "millionaire". The KV-2 was not a replacement for factory #212's SPGs, but a supplement.