"If the overworld is so good, why isn't there an overworld two?"
Overworld Two (Forge) is a port of the fabric optimization mod "Overworld Two" 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!. 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.
Ore generation optimizations are global across all world types if the config value "fast_ores" is true.
Disclaimer: This is a port of the original mod Overworld Two from fabric to forge. I(CorgiTaco) have been given consent to port this mod by the original authors(Gegy1000 & SuperCoder79) w/ the agreement to maintain it myself. This mod may not be updated in conjuction with the original fabric mod and will only be updated when I find the time to do so.