The ocean floor is too flat and lacks terrain variation (hills, valleys, and elevation changes). Additionally, the spawn rate of shallow areas (shoals) is excessively low. These issues make the ocean biome feel unnaturally empty and monotonous.

Tectonic DataPack

Vanillan

Will address this once I can toggle on blending to existing worlds.

Ocean terrain overhaul will be included in Tectonic 2.5!

Not sure how much more of this you're interested in implementing, but "underwater rivers" could be a cool terrain type for Tectonic, and a good excuse for underwater canyons in a generation schema which is normally very bad for them if implemented between coastal areas and deep ocean biomes.

Generally IRL they come out of the mouth of river deltas and continue further down, until they hit the continental shelf dropoff and drop their payload off into the deep ocean, carving channels into the shelf as they go. You probably don't want to go as large as some of the topographical maps, but I think it would be an interesting ocean terrain.