I seem to remember that people were complaining about how easily warp gaurdians could get in, and before players could notice, launch waves to otherwise non-border planets.
So the devs compromised and added an alarm warning when a warp gaurdian gets angered (and I think also having certain amount of time after angering before their "warp" property becomes "active", but I could be wrong about that). In return, they 4x their HP and attack. As mentioned by several posters, 4x was a bit too much of a buff for them, not worth the "must announce themselves" nerf they got. Maybe half all the stats that quadrupled, giving a net 2x of what they were before the announcement thing. That seems a little more reasonable.