Deepslate blocks aren't mined any faster while affected by the haste II beacon buff. The beacon buff still works fine on the 'Tuff' block.
Comments 2
I’ve had the same problem on version 1.21.7. After building the full beacon with Haste II, deepslate wasn’t affected. It wasn’t like “faster, but still slow”. I tested breaking the beacon and reactivating it, and only other blocks (not deepslate) were mined faster. The mining speed for deepslate was the same.
Haste 2 does allow you to mine deepslate faster than without it, it just doesn't get fast enough to the point that you can instamine
This is intentional, deepslate is just a tougher block than stone
Not a bug