But it's important to note that before the Iowas were given their final retirements into museum ships the Navy made sure to basically document everything they could about firing large caliber guns. Because when they initially pulled them out of mothballs in the 1980s they were woefully inaccurate, but by the time they were decommissioned for the final time they could hit a proverbial fly on a flag pole (allegedly).
The other part of it was that the Soviet Union didn't really have a surface fleet to really speak of. They invested heavily in submarines, so consequently the US Navy focused heavily on ASW. So... nobody really knows how 16" of modern armor would fair against modern weapons, it's literally never been tried. Whereas you can find pictures from way back when they were testing guns, of how various shells fared against various thicknesses and types of armor.
Long story short: We've forgotten most of what we knew about surface warfare, and we're starting to forget what we knew about shipbuilding and design. The US has outsourced all it's naval architecture and shipbuilding so long that the necessary skills are either all retired or lost.