Pirates didn't make their appearance for a couple of years, but the point is not whether they were available or not, but rather if the overall model is lessened by the choice that Lego made. It's not a detraction to me now since I have more oars than I know what to do with.
I guess in hindsight the spears as oars are a problem. But it is like giving 375 knights one piece horses - a very good idea but not possible when initially released.
I think making a comparison is fair - it doesn't matter when they were made.
A comparison can be made but it is not a strong one. 6057 has much more in common with Emperor's Ship than 6049. (http://guide.lugnet.com/set/7416)
I agree with you that 6057 could be better for a legend. But I think 6049 is very good for its much smaller scale. It is a "crusader canoe"