I created a custom world by adjusting the "continentalness" setting to enlarge oceans. I edited 7500 biome settings in minecraft/dimension/overworld.json and 18 noise settings in minecraft/worldgen/noise_settings/overworld.json. This worked fine, except the spawn point for the world was in the ocean.

The spawn point matches closely the spawn point for the unmodified world with the same seed. It appears the algorithm for spawn point is not taking into account these changes to the terrain generation.

To reproduce:
1. Create a vanilla datapack, or use this one: https://drive.google.com/file/d/1OyLG704MKEILKQGY9utUreFms7G7v2jw/view?usp=sharing (described here: https://www.reddit.com/r/minecraft_configs/comments/rbfyay/i_set_up_a_vanilla_118_worldgen_datapack_template/).
2. Copy the altered files to the correct locations.
3. Start a new world with the datapack. Give the world a seed of 1. --> Player spawns in the ocean.

Suggested fixes:
(1) When searching for the spawn point, remove hardcoded settings and take into account any changes to the terrain. A possible way of doing this is to expose the settings for the spawn point algorithm. For example, if the "continentalness" for beaches is changed from -0.15 to +0.30, it should be possible to configure this for the purposes of locating a spawn point.
(2) Searching for the spawn point should not use steps of 16 at all distances, but use larger steps farther out. This could locate a spawn point faster, at the cost of lower precision.

Attachments: dimension.overworld.json, worldgen.noise_settings.overworld.json.