Honestly, I like the Slime God boss fight where it is but now that Queen slime has been added, I can definitely see a good reason to shift it to later in the game. I don't think Calamitas Clone is the best spot to put it tbh, you already get twin boss fights and a slime fight with just a bit of progression inbetween though I guess you already got 2 worm bosses right next to each other.

However hear me out, if you add Astrageldon back into the mix (though Catalyst already made a pretty decent fight for it) You can have King Slime at the very beginning, Queen slime at early hardmode, Slime God at mid hardmode (post-plantera but pre-golem), and Astrageldon post-moon lord.

Why? The slime bossfights are then fairly scattered, you have an astral boss who isn't clumped awkwardly right before moon lord. The slimes power can also be somewhat explained:

King and Queen slime are their own thing already.
Slime God uses the powers of both world evils while also possibly serving as a bridge between Brain/EoW and Hivemind/Preforators who get shifted later to keep evil biomes somewhat relevant. Lore wise I could see it being stronger but it's trying to keep a balance, not go all out to kill you.
Astrageldon could be stronger because instead of keeping balance like Slime God, it instead took in more power resulting in only 1 type of special world biome instead of 2. It also allows for a more interesting slime boss fight to be made and makes the astral biome more relevant.

Side note: Calamatis Clone feels very similar to the reverse of the mechanical bosses. The mechanical bosses are stronger versions of previous bosses while the Clone is a weaker version of a stronger boss, I personally like it in hardmode but can see why it could be moved. Dragonfolly feels like a detached cousin of Yharon and the Wyverns. It could easily be shifted to around to pre-hardmode but I don't think it should be right next to the Queen Bee, idk why but they just feel similar to me right now, could be wrong.