Make in-map alith defense events less common vs "regular" breaches

It's pretty clear somebody at GGG *really* loves tower defense, but the last thing I want when running a map is more mechanics that go "Okay now stop and stand in one spot for a minute or you get nothing from me". It's boring. I get having it around to some extent to introduce people to the hive fortress tower defense but it's not a fun mechanic in a map and it should be scaled way back in how often it shows up compared to the more tolerable unstable/stable breaches.