A SETI attack may be faster in terms of latency, but that doesn't matter unless the variance in development time is very low.

I think that you are understating the importance of latency. Earlier, in this post you pointed out some of the difficulties in a civilization 1480 ly away launching an attack on Earth's civilization due to the distances involved. It seems to me that a SETI attack would eliminate these difficulties; the attack could be launched with no knowledge of Earth or Earth's civilization whatsoever, so the attack would not have to wait 1400 years for our radio signals to bring us to the attention of a (hypothetical) advanced civilization. And, a SETI-type attack would not require expensive and time consuming vehicular scouting/probe missions.