Aaand you can do suboptimal rotations and still complete LFR. You don't need to do an optimal rotation to complete LFR, this is why I feel like Proving Grounds at least shows you can somewhat handle target switching, tank cooldowns, etc. You don't need to be skilled to do Proving Grounds or LFR, but you at least somewhat need to know some basic mechanics that I feel like Proving Grounds at least shows you or teaches you about.
I had an argument against that, but I'm too tired to remember it. I guess you're right to a point though. Either way, I feel like requiring PG silver (or anything for that matter) to get into LFRs is silly and won't change anything. As I've said before those who put in the bare minimum will still put in the bare minimum and those who do not will continue to put effort into it. It's just the way raiding works. Not just LFR it happens in normal/heroic raids as well. Only difference is LFR is the only difficulty where you have to deal with it.