[NAG3LT]

The market is moving towards MILC, including Canon's and Nikon 's top sports bodies (R3, Z9). With fast sensor readout and improved processing power, they will focus better than 1DX3 and D6 in most circumstances. Both with grips and larger batteries. They won't match DSLR at idle battery life, but the differences in shots when taking many bursts will be much smaller than CIPA suggests.

Technological replacement happens when new tech has important advantages over the old, without needing to outperform it in every single way.

[geerlingguy]

They may not focus better in every scenario, just 'different'. And I've found there are certain types of photography where focus on even entry-level mirrorless destroys the DSLR experience.

But for sports and wildlife, you do need to get the highest-end bodies for a pleasant AF experience that can match the high-end DSLRs like the D850, D500 (which IMO were basically 'magic' in giving keepers once you understood the system).

The bigger advantage with mirrorless, as the image processing pipeline catches up, is the ML algorithms that can run on the entire image giving more control over focus tracking in weird situations, where the more optical AF systems in DSLRs don't have as much data to build from.

It's crazy how good AF got over the years on DSLRs, and it's also amazing how quickly all three (Sony, Nikon, and Canon) have put together competent AF pipelines in their mirrorless bodies. Sony leads here a little, but just barely, and mostly because they were all-in on high-end mirrorless before Nikon or Canon really got serious.