I hear what you're saying, but I have about 200 games stored on a traditional HDD that only provides me a read speed of about 220MB/s absolute maximum and I have never had a single issue with any game running from it. As you say this could become a problem as devs adopt directstorage but as it stands right now, it's a total none-issue.

I have a 2TB NVME M.2 drive in my PC but don't really see any advantage to putting games on there, that's what bulk storage is for. If you are playing online, 99% of games will have a countdown or otherwise make you wait until the slowest PC is also ready to go. If it's a game that uses loading screens, I really don't care as it still loads pretty damn fast.

Pretty much the only games that I will throw on my M.2 drive is open world games that load as you go if I am on my first playthrough. RDR2 lived on there for a while.