"If the overworld is so good, why isn't there an overworld two?"
Overworld Two is a fabric optimization mod that generates overworld and nether terrain much faster than vanilla minecraft at the cost of breaking parity: that is, the same seed in vanilla will generate differently with this mod installed!
Some basic results show that it reduces world gen times by up to 50% on servers, and even more with Lithium and Phosphor installed. To access Overworld Two generation, you can use the world type on the selection screen or use the level type "overworld_two" on servers. Nether generation is enabled by default but can be turned off in the config. You can visit the Discord server to discuss the mod and receive support.