Freshwater fish have a much less robust ratio of omega 3 to 6. Inland peoples probably ate as much freshwater fish as they could catch, but they would not have gotten nearly the same omega 3/6 ratio from it as those who ate certain saltwater fish. So no, I don't think inland peoples relied on fish for their omega profiles.
Also, I think that research still needs to prove that intake of omega 3 can cancel out intake of omega 6. I have yet to see research that differentiates the benefits of just eating less 6s to that of eating more 3s and less 6s. My point is, most benefits may be due to simply decreasing levels of 6s overall. Also, people taking fish pills and eating SAD may benefit simply becuase they don't have enough fat in their diets in the first place. Jury is still out, IMO, over how beneficial it is to eat lots of fish oil if you are already eating a healthy diet otherwise. Certainly, I have heard of some people feeling really sick after eating lots of fish oil pills. And most people not noticing any obvious changes at all.
Also, could be simply that omega 6 containing foods might be unhealthy for other reasons besides their 6 content. The amount of 6 may not be the main point. Those who eat very little 6 also happen to be those who eat whole natural foods, limit grains, etc. The prob with epidemiological studies is that they can't show causation. We only know that omega 6 intake seems to be CORRELATED with various problems. We don't yet know how much the 6 is directly responsible vs other crappy parts of those same foods that contain the 6s.
Sooo, I think the jury is still out on the benefits of sea fish oil intake. Certainly, many populatoins have been very healthy without any seafood at all, just freshwater fish, so sea fish are not a requirement of healthy living. How much sea fish might contribute is, IMO, still up for debate and I will keep a skeptical and observant eye as research continues..
Also, my advice for learning to like fish, get yourself a fresh caught fish like righ toff the dock and still flipping, no more than a day old. Those kind taste WAY WAY WAY better and are not stinky. Then have someone else prep it for you so your brain does not scream FISH when you look at it. Fresh fish is at least twice as good and way less fishy than the kinda old fish from the average grocery store. I am a bit lackluster on fish myself, but when I ate a fresh caught bass cooked in nothing but butter, I found myself guzzling it down with incredible gusto. It was a very different experience when it was fresh.