Customized world generation was removed in the development of 1.13, stated to be a temporary change. So far, there were no news about its reintroduction, and there are no ways it could be tracked. I feel like since Minecraft is a sandbox game, it shouldn't be an issue to make some hardcoded values changeable, at least in the level NBT, similarly to the vanilla_layered option. Together with the buffet option and setting the main world generator, it could be used to create incredible worlds like lava caves, completely submerged worlds and others. The options to toggle the generation of certain structures is also sorely missed.
50 sliders are completely fine; usability shouldn't be traded for simplicity.
Thank you for your report!
However, this issue is Invalid.
You have posted a feature request or a suggestion. This site is for bug reports only.
The developers are aware that many players want customized worlds back. They will be re-added soon™.
Quick Links:
📓 Issue Guidelines – 💬 Community Support – 📧 Customer Support – 📖 Game Wiki