Look at the crap the average American eats. All the bread, chips, candy, soda, alcohol, hydrogenated oils and rancid vegetable oils, lunchmeats, fake cheeses, cake, cookies...paired with the stress of a 40+ hour workweek, little to no exposure to sunshine and fresh air and little exercise and it STILL takes 70+ years for all this crap to kill you. You are eliminating almost all of this by "going Primal."
I see little issue with grain fed meat in the grand scheme of things. Compared to all the horrible things modern humans do, and it still takes decades to catch up with us, this is a drop in the bucket. Eliminate the bad stuff - grains, legumes, polyunsaturated refined vegetable oils, refined sugars and chemical/preservatives/thickeners/additive - and you are so far ahead of the game you can enjoy your cheap corn fed steak. That's what I do and I don't think it's an issue. If you have the money, buy the good stuff, if not do the best you can. Giant has angus bottom round roast buy one get one free this week. I'll be stopping by.
Don't put your trust in anyone on this forum, including me. You are the key to your own success.