Fellows,
If you owned ne of those company, you will have the same attitude.
So let move on like one of this fellow said, a lot of photography in front of us until Jesus come back, stop crying and go with the world, even we are not from it but we have to live in it - Have a Blessed and wonderful day plus ther will be Pro Football this Thursday night, what a great country still. Be Blessed guys.

You can use them, but you have to buy a connector. I have used them for 3 years now and everything go good. I use R-6 with EF 24-70 and also EF 70-200. NO PROBLEM whaat so ever. buy the connector that $100,00; do not buy tyhe most expensive one.
Try it and you will ilke it. Have a Blessed Day.

If you really only want to have one, wait for Canon EOS R6 and put a 24-70 mm RF lenses. Thats it, but stay with it put britle like horse and only look forward. God will Nless you.