It's a commonly acknowledged fact among all sailors - professional and recreational alike - that wave height can vary greatly depending on other factors, even if wind speed is the same at two separate moments. And for example, I've seen wave height of over 1m in wind conditions that would've normally caused only about 0,5m wave height in the Finnish Archipelago. In that case the cause was strong winds that had been blowing for the two earlier days, which still caused the sea to be quite rough despite light winds.
So the separate wave height slider would in fact allow for much more variety while still remaining perfectly realistic. And even more realistic than current situation which only allows for one kind on sea state for a given wind speed.
I would strongly welcome this addition!