I am sorry if it's stated elsewhere, but what exactly triggers the enemy to attack? So far i was under the impression the same rules apply of "pollution touches the enemy, they now become aggressive". But i have lost 2 worlds now because out of nowhere, a horde of super enemies appear and just steam roll through my bases. And if that wasn't bad enough, what follows is constant spawn kills that is almost instant.

I literally have radars all around and no bases appear that are touched by the pollution.

lol. Yes. There are other triggers other than pollution. The custom attack wave sends a larger group under those triggers. You can read more about them in the "Attack meters / Custom Attack Squad" in the information page.

Here are the TL:DR version.

1. Revenge attack wave. It's based on attack points, which accumulates when you kill the enemies. Once attack points reach its threshold, it sends out a custom attack group which is about 1.5x size than default group.
2. Timed based attack wave, this adds attack point every minutes until attack point reach its threshold. It then send out an custom attack group once threshold is reached. By default, it's 2% of threshold per minute. But it's not going to take 50 minutes to spawn a new wave, because you will likely be killing them in that period. However, time based attack don't start until enemy reach level 3.
3. Launching rockets and using super weapon(nukes) also add additional attack points.

You should research weapon tech as priority(especially bullet upgrade) and get construction bots ASAP when you play with this mod.

If you find that custom attack waves are too much to handle, you can turn them off in the map settings until you are ready to face them. There are many settings that you can tweak how custom attack waves behave as well.

---- And if that wasn't bad enough, what follows is constant spawn kills that is almost instant. ----
Ya. It's game over once they camp at your spawn point. It sounds like you need a lot more heavier defense.