Reading your post I'm reminded of the Shwerer Gustav which were the biggest canons ever made, shot a 7 tonne 3.6m projectile and obliterated basically any target of the time.. Objectively impressive.
However.. the Germans only built 2 of them and it took so long that the battle they were explicitly designed for was well over by the time they were completed, only 1 was ever fired and wasn't really needed for that battle either, they cost $7m Reichsmarks each (~$62 mil USD in 2025), 1400+ tonnes of steel, required a crew of 2,750 and two flak battalions for protection (~2000 additional men). Not so great when you read the fine-print.