Merge casters

Given how some other buildings work, it seems like a kind of weird relic that the metal caster and cooled caster are separate buildings and that the cooled caster can only do steel. Wouldn't it make more sense for those to be a single building with optional water input, and possibly to be able to cool iron and copper to get them done faster as well?
On a similar note, the "II" levels of these buildings also give me a... "why is the throughput higher?" vibe. I know at base the reason is "to be able to keep up with the blast furnace II with in-place upgrades", but it's a little weird since there's not much you can really do to make slabs of metal cool twice as fast. It could at least be vertically bigger and have doubled capacity instead of speed... or keep water-cooling separate as the second tier (maybe with chilled water as tier II cooling for steel?), or something.