Maybe I'm just blind but there used to be setting for frequency of deep see oil I can't find it anymore was it removed?

Sea oil now spawns with the same frrquency as land oil, using the same map generator controls. You can disable land oil or sea oil entirely, or make them different richness, but cannot have them with different frequencies. It's remarkably hard to make resources spawn only in water, so this was a work around.

"Sea oil now spawns with the same frrquency as land oil, using the same map generator controls."

Does this still apply when using RSO?

I believe so, but I haven't tested much with RSO. On my to-do list was talking to them to see if there is a better way for RSO to spawn deep sea oil by itself.

What it does now is wait for each chunk to generate, looks for crude oil spawned on water (it can spawn on both land and water), then converts all the crude oil deposits in the chunk into a single deep oil deposit. It should perform this after both vanilla and RSO have completed spawning crude oil entities.