Because you had to use the word "becoming" and not "equal". When it matters at those frame rates, the mirrorless doesnt keep up.with mirrorless aps-c doing 20-30 fps now and becoming a real competition when it comes to focusing.... why buying a mirrorslapper?
i would love to see a high-end mirrorless aps-c with 20 fps and great focusing for BIF.
I used Sony for a year or two, and between the menu system, the auto-focus, the terrible battery life, the mediocre screen, and the overheating, it was a nightmare to work with. They're fixing those issues, for sure, but the XXD line has just worked for the entire time I used it. First as the 60D, now as the 80D. I'd gladly take a 90D that costs a little more but has the 7D weather-sealing, some of the 7DII's auto-focus options, a bump to like 10fps, and having 4k.
And if Canon cant deliver that, I'll do what I've already been leaning towards and just move Panasonic.