Better to have 2 ships that can be in 2 places and have the same combined firepower even if the combined cost is somewhat more
They died out for a completely different reason - it was more profitable to put 203-mm on the Brooklyn hull. That's what the Americans did in reality, building a heavy cruiser based on it. And the Japanese simply provided for a replacement already at the design stage. This is to the question of "cruisers with 203-mm were needed only because of the contract
The problem is that one "doubled" ship will kill both competitors like cockroaches with a slipper. Even if we assume that its armament is just as light (just twice as many of the same guns).
1. "Gulliver" is twice "stronger". By concentrating artillery fire on one of the "midgets", he will drown one of the opponents twice as fast as they could drown him in the first approximation. At the same time, no one promised that the opponents would have time to disable half of his weapons.
In the second approximation
2. The Gulliver is a more stable artillery platform and it has physically better sights (the masts are higher and the rangefinder base is larger). As a result, it shoots further and more accurately in general.
That is, in reality, the ratio for midgets will be much worse.
But this is a theory. In reality
3. Gulliver at equal power... somewhat faster. 1) It is shorter than those two combined, which means it suffers less from friction resistance 2) but longer than each one individually - and suffers less from wave resistance.
4. Gulliver has a better surface/volume ratio. As a result, the armor is thicker, which creates a dead zone where he breaks through the armor, but the midgets do not.
In combination with 2. - this is an unpunished execution.
That is, Gulliver is bad for control, but good for direct combat.
At the same time , this regularity is especially obvious
will be 1) for armored ships. 2) with long-range artillery.
However, in reality, you can put a large cannon on a large ship, and in combination with 1 -2. this will give a multiplicative effect. Unless, of course, you are bound by the Washington Treaty.
Hence the whole kiloton race, especially after 1905.
Also, what is the realistic doctrinal use for such a ship? I mean, sure, you can lay down a hail of fire against enemy cruisers and destroyers. But that's about it. You'll still be unable to fight larger things like battleships and battlecruisers
1. Actually, this consideration works even better with light cruisers. They have a range of "convenient" goals even narrower.
2. In fact, he can. A 203-mm projectile relative to even a 410 mm cannon is about 152 mm versus 305 mm at Tsushima. Not a completely useless thing. But 152-mm cruisers turn out to be in the area of the then "scouts" / aviso.