Havoc grenades are bad because they are going to destroy spawns under fire. Instead of having a good contest of trying to keep or destroy a sunderer, with the Havoc grenades, the deployed sunderers wiill just die fast. At least w/ the NS-66P Underbarrel it wasn't too OP as it was sometimes still difficult to get a shot. Now that most likely all the heavies will be carrying a Havoc grenade in the actual game, sunderer spawns have no chance.
If the enemy has enough concentrated AV fire on the spawn that you cant get rid off and you can only try to outrepair it, the Sunderer is dead 9 times out of 10 anyways. I think Havocs would be a niche option, mostly used to break MAX's who rely on the repairs to hold their ground. Otherwise an AV/frag would be a better general purpose option, not to mention good against Sunderers by killing the repair crew or damaging the Sunderer.
oh yeah, it would destroy Maxs like that. Maxs hardly get used too and not everyone repairs them. Perhaps Maxs should cost half they do now and have 1/3 less HP to make it balanced. A couple vehicle/air pulls to drop the spawns or even a fury flash would destroy the sunderers. Repairing the sunderers underfire is a collective effort and not impossible to take down. Havoc grenades would ruin this significantly and the logistics effort of putting good spawns would be gone. There is a significant amount of fun trying to hold off from an overrun for a bit. I think it could be a good idea to experiment with having havoc grenades that disable repairing in the game. It might not even be an experiment, it could probably last forever. 6 seconds is going to be way too long especially near and inside tight control points. If this is happening 100% Maxs should cost at least 1/3 less in nanites to have than they do now as they should die fast.