In regards to seaworthiness of SOT vs Sit In kayaks, it depends...
Typically a SOT, because you are sitting on top of a air cavity of some depth, will have a higher center of gravity and in that sense be more tippy than Sit inside. Initially the SOT will feel more stable because its like a big surfboard compared to a sit inside sea kayak, which is narrower, but when a sit-inside goes, it goes suddenly. It has little reserve stability.
If you do swamp or flip a sit-inside sea kayak, (and are unable to roll it back, which takes considerable strength and skill, )attempting re-entering a sit-inside, often full of water, can be difficult. A SOT can just be climbed back on (by most fit people anyway) like a surfboard
Some specific hull shapes, available only in sit in sea kayaks ( e.g. Icelandic) , seem tippy at first, but stiffen up when leaning, and have good reserve stability. This type of sea kayak can offer more control in terms of maneuvering it begins to become unstable.
So given a unexpected wave, I think you are more likely to find yourself in the water when you paddle a SOT, because of the higher center of gravity, the lack of secondary stability, and the less optimal hull shape of SOT in regards to controlling the kayak.
But given that you suddenly find your self in the water, I think you are a lot less likely to be able to get safely back into the Sit Inside than the SOT, especially if you paddle solo.