While fighting the warden, build a tower two blocks high, crouch, and stay roughly centered on the tower. Your crouching prevents you from being knocked off by his boom due to the shallow angle. This allows him to be trapped standing still in your melee reach. Eating subsequently nullifies the damage of the warden boom. Here someone demonstrates the issue:

https://youtu.be/ni3Oq31jQY4

Proposed fix: Add back Warden extended melee range or make sonic boom have a special exception bypass the protection enchantment. This will allow the warden to be much more difficult to cheese. When you must build higher to avoid his melee range, the angle is steeper, and you won't be able to prevent yourself being knocked off by simply crouching.