I'm not entirely sure what the purpose of your argument is. It's fairly obvious the Empire has never given a rat's ass about 'cost' or 'manpower'. Their only concern is "does it kill what we want it to", and it did. The questions of cost etc. were all raised in the now defunct EU and supposedly an Imperial concern where everything we see about Palpatine's military pomp and gloria points towards a man who can afford it. Seriously, how is something the size of a moon, or repurposing a planet, somehow more expensive than maintaining an entire galaxy? The idea that something so small as the Death Star or even Starkiller Base would make a dent in the finances of a military machine that can call upon the taxation of hundreds of thousands of civilised worlds is ludicrous.
It does when you get to fire it a couple times and then the people whom it is supposed to cow into submission blow it up, and you've wasted enough resources to launch scores of far-more-practical and useful ships.
Furthermore, the destruction of Alderaan just turned more people to the cause of the Rebellion... it was a net loss in the end.
And Starkiller base remotely destroyed the political and military centerpoint of the New Republic, which is going to cause unimaginable chaos, while pinning the blame on the Imperial Remnant (let's keep in mind the NEW REPUBLIC doesn't know squat about the First Order).
But yeah, let's equate it to the Tarkin Doctrine, which didn't even apply to DS2, and call it a failure, sure.
At this point, I'm fairly certain you just never liked the Death Stars in any movie, and your kneejerk reaction is putting you in full false equivalency mode, same as the people who somehow think Kylo Ren should be Darth Vader. Take off your goggles and watch the movie, not what your preconceptions think the movie should be .
Ah, OK, we're at the point in the internet argument where you fall back on ad hom and start trying to imagine what my unstated motivation might be so you can put on smug airs and start telling me to "open my eyes". Keep your advise to yourself, but the attitude is noted.
For the record, the first Death Star wasn't an issue, between Palpatine and Tarkin it made some in-setting sense... a massive showpiece statement in their doctrine of rule by fear and an unintentional symbol of their arrogance.
After that, the concept has failed, Tarkin is dead, and Vadar was not a proponent in the first place, so in-setting, doing it over and over makes little sense. In storytelling terms, the original trilogy tapped that vein twice, and all the subsequent appearances of "galactic WMD" amount to writers falling back on formulaic repetition.
Edited by MaxKilljoy