Drained buildings should keep the same HP in the next phase (idea).

[OrionZG]

There is still some numerical disadvantage between the defending and attacking clans, specifically the latter.

It would be a good idea for buildings that have been drained in one phase to keep the same HP in the next, for example, if a level 4 building is drained to 30k HP in the first phase, then that building stays with the same HP in the second phase, and so on until it falls or is repaired.

In this way it would give the attackers to actively participate in drains, and have a second/third chance in the later phases.

 

[OrionZG]

And another thing to add, the building can receive +5-10k HP in each new phase to balance the defender's side.