D-Wave works both in attack and defence, but as a defensive tool it is pretty weak. The reason is that it only disables the abilities that affect combat value, specifically:
- Empath and Soporific Gas on the attacker
- AAA, Trance and ECM on the defender
Of course, disabling Trance and Empath is only useful if you have Psi weapons or armour on conventional units. The big killer is disabling AAA, especially considering that defensive D-Waves do
not work against Nerve Gas.
But I do not consider it a game-ender. It lies on a not very popular research path in MP, and by the time you get it, your opponents are likely to have Tachyon Fields, which gives them a very good chance even against an X/Wave chopper.