If forts were built along the path (like the Eyrie in GoT) Hrothgar would be near unassailable.
Or just delaying the inevitable and making it so they can't leave thus really it becomes nothing but a huge trap.
1. There's another supplier outside of Windhelm, forget her name. East Empire Co is the familiar face but its not the only kid on the block. Besides, I totally raided their supplies.
2. Ysgremor didn't have no problem with Elves....Seriously though, I think people play on the lore of magic a bit too much. Its important and powerful and all that yeah. But I don't think its correct to say that magic > all. I think people tend to glean to heavily on the magic lore. Truthfully, ranged combat can be done just as well with trained bowmen.
Counter question. The Elves feared the Nords rate of reproduction in the early days of Nord presence on Skyrim. This tells us, Mer cannot recover as quickly from war losses as Men. If both sides faced heavy casualties following the Great War, couldn't it be possible that in the 25 some odd years since the end of the great war, that the forces of Men have recovered to a considerably greater degree than the Mer?
Too address your first one, that shipping company relied too much on pirates for business, once the EEC is gone whose to say the pirates wouldn't hit them harder? Thus ruining the business because they can't afford to exterminate them.
Second, yes ysgremor never had a problem with elves or magic but that doesn't change the fact that if something goes wrong a lot of Nords will either blame magicka and mages (like in the great collapse and proof of this furthers with several nords showing distaste towards you asking about the college or Fallion up in mortal), Falmer who are seen as entities of malice and bad luck as well as stealing children and murdering farm animals as well as causing blizzards, foreigners, yes I know this is a touchy subject but there are nords that will blame foreigners for problems.
also towards your elf question, not all elves are like that for example its been hinted that Orsimer and Bosmer reproduce as humans do while Altmer do but theres some believe that the Altmer kill their young at the sign of disabilities and imperfection as for the Dunmer they reproduce slowly and its often said that most go their lives with only having 1-4 children.