I don't see an issue with this either if you are making it yourself and actually making biltong
I would be surprised if the majority of meat eaters would agree. You may be right but grass fed animals are frequently described as gamey which many folks don't like. I eat more wild game than beef so I do like grass fed beef although it's a little chewier due to less marbling than grain finished beef which I also like. Grass fed "flavor" can be concentrated in fat so depending on the percentage in ground meat it might be too strong for some.
Alfalfa or corn or soybeans would be the most likely GMO crops to reach a domestic steer. I'm absolutely positive I could not tell a difference if it was GMO or non-GMO when it comes to the meat taste.
GMO vs Non-GMO and organic vs inorganic are really philosophical decisions. All other things being equal (feed, freshness, etc.), there are no taste differences or provable health benefits to either. You’d think maybe there would be, but the differences are not really demonstrable.
I used to say the same about the gamey taste, especially when I lived out west in the high deserts. But since moving back to Missouri, there are many times I'll cook up a venison steak or roast and have a very tough time telling the difference in taste and gaminess between it and beef.
As for GMO, I was referring to animals that are given growth hormones (steroids) to enhance their size and weight, especially in chickens where the breasts might be nice and big, but most of the time they're dry, tough, and pretty bland taste. For beef, it's the taste of the fats especially in ground meat where I notice a difference in the taste, with the "enhanced" cows having a noticeable and to me unpleasant aftertaste I don't get from naturally raised and bred cattle.
I will say that the Trader Joe's extra lean ground beef tastes significantly better than other commercially available brands and the quality is quite consistent. That said, I recently discovered a local butcher who sells me raw meat for my dog and I have since moved to buying my ground beef there.