I don't think Death Star is an equivalent for the senate or any kind of seat of power. The closest equivalent is British navy in the 19th and early 20th century. It was used to keep control of the subjugated land across the world. If someone resisted they would use the navy to spank them. King was still in London.

And certainly half finished DS2 wasn't safer than Coruscant. Emperor didn't come on unfinished DS2 to be safe. The only reason Emperor came to Endor was to get Luke (and possibly destroy Alliance in the process).

Since some fans say the imps shouldn't build DS2 because clearly the first one was proved weak. I mentioned 20th century navy. Post WW1 battleship building is a perfect example of man being capable of building extremely expensive and at the same time useless things over and over again.