They are much better now. The pro I know went from a canon 5D mkiii to mirrorless R5? (Classical performance photos). It’s quiet fast and the new lenses are better/smaller. The lack of A mirror means it’s faster as it doesn’t have to physically flip it up to take the picture. They’ve embeded the focus sensors on the image sensor so it’s much faster focusing than previous mirrorless[1]

[1]https://www.dpreview.com/forums/thread/4703538

The downsides are price and battery life, and if you have existing lenses you’ll need an adapter..