How do you quantify what is "okay" performance?
I can guarantee you that players would try to set the bar for "okay" far higher than the developers have set it. Many already get upset when a dungeon isn't facerolled in 10 minutes.
What do you do about the players using systems that meet minimum system requirements and/or have slow internet connections speeds because they live in remote areas? Do you say "tough for you, you aren't allowed to play because you aren't rich enough to have the latest tech and fastest internet"? I remember raiding in WoW back in Wrath. My computer died mid-tier, got a replacement 2 weeks later and went back to raiding with the guild. My DPS increased 30% not because I had suddenly become a better player after 2 weeks of not raiding but because I was no longer having to raid at 3-7 FPS. Skill queuing was working better for me and I could see mechanics in enough time to move out of the way consistently instead of just when I got lucky.
Then there are the overseas players dealing with much higher ping that face the same struggles I had back in Wrath despite having good systems and good connection speeds.
It's difficult to set standards for what is "okay" when every player's situation is different. If you personally don't want to play with those who struggle for whatever reason, that's your choice. Use PF to form groups instead of relying on Duty Finder matchmaking and you can set your own standards for who is in your group.
But it's not up to you or any other players to decide who should be allowed to play. That's up to SE.