600lb Deadlift Possible for Everyone?

I don’t think so. Some people could if they wanted to gain a huge amount of body weight and get up to weighing 250-300+ lbs. Think of it like this: deadlifting 2x your bodyweight is doable for someone who trains and gets pretty strong (completely natural), but is nothing spectacular. Still, there are lots of guys who can’t DL 2X their BW. That would mean a lot of guys would need to get over 300 lbs to do that lift.