A massive object flying at a substantial fraction of the speed of light would be better for communication over very long range. Sure, the overall latency would

A massive object flying at a substantial fraction of the speed of light would be better for communication over very long range. Sure, the overall latency would be greater, but a massive object doesn't suffer from the inverse-square law if you know where you want to send it, and doesn't need a larger antenna to make it more directional. If it's some kind of programmable or even intelligent machine, then it could adapt to the evolution of conditions at its destination upon arrival, and engage in many iterations of short distance communications before sending data homeward. It's like why we sent human envoys during the era when communication speeds were limited by horses and ships. ET has probably given up on long range radio for their local comms, just as we have. The bulk of our comms go through waveguides (electrical cables and optical fibers). Even our radio comms have relatively short range, and are designed to be virtually indistinguishable from noise. It's as if we've wrapped ourselves in a primitive Dyson sphere.