We cant say how much. The increase in block between the hive scutum and the alexander tower shield might not even increase it 28% to 29%.

Certainly its interesting that it scales, but you would also note that

dark dance: 20 seconds up, 40 seconds down.
bulwark: 15 seconds up, 165 seconds down.

These arnt really comparable. Dark Dance just for the 30% parry is great, and when the 20% dodge applies is fantastic.