"SEAWORTHY" is a poorly defined term. If someone tells you that a boat is more (or less) seaworthy than another boat ask them to tell you precisely how the boat will behave in rough water and why this is good, or bad. You may find that many people don't seem to quite know what they are talking about.
I don't claim to be an expert but my thoughts on shorter boats:
Lighter....easy to carry up the beach.
Carry less cargo....could be bad on a long trip. you could be tempted to overload them.
You may feel that the waves tend to "knock you around" more. This is just the way I felt the few times I have paddled shorter boats. Each paddler will have to decide for themselves.