Check out the release notes, it explains the thinking in great detail -- there should also be some very long topics about that in this forum if you search for golems. They definitely aren't overpowered, if anything people are still somewhat thinking they are too expensive to be worth their time strategically. But you are correct in that they don't come with permanent ongoing costs anymore (the AI Progress), which was a goal. Almost no one used golems in the past, and this has been a continual reminiscing to get our risk-averse commanders to use them.
The effects of the golem on waves, like the 3X waves, etc, are just on the planet they are on, not global. The main drawback of the golems are that they are insanely expensive both to build and then to maintain. For the equivalent firepower with convention ships, you could spend a lot less metal and crystal. That actually is also by design at this stage, so that golems are not obvious go-to things to capture, but if you are already capped out on your regular fleets, etc, they make an
excellent secondary investment (though some people still prefer mercenaries, it varies).
