Sensor readout speed is a mostly fixed parameter. What can happen is that the processor speedcan increase to shorten the data processing pipeline time. The S5 has the same sensor as the S1 and S1H (and Nikon Z6, Sony A7III, Sigma fp, Leica SL2-S etc.) but it had updated AF algorithms that all of the Panasonic cameras have now. I’m not sure how the Leica SL2 compares speed wise but maximum speed and accuracy can be had with single point AF or to just trust that the DFD is working (which it usually does even if it doesn’t appear to be). It’s disconcerting for sure coming from Sony but it’s a matter of trust. Also when you customize, I found that making some of the custom buttons to be near/far focus shift greatly increases accuracy to where it gets somewhat closer to being as reliable as Sony for tracking people or animals for photos in those zones.One thing that needs to happen in Panasonic AF (as long as they stay DFD contrast based only) is to increase sensor readout speed. This obviously happened already with the S5 and will again (hopefully) happen with the GH6, as this one will have a completely new and redesigned sensor.
While testing the Leica SL2 earlier this week it was pretty obvious that the SL2 AFC (face and body) is not as confident and fast as even the Nikon Z7 AF and this is known to be not the best AFC. And the Leica uses that same Panasonic technology. So they need to work on this and it will be interesting to see what their new GH6 will be able to deliver here. It should better be a real big upgrade - hopefully.
But maybe a miracle will happen and they decide to go also PDAF in addition to contrast based like all the others do.
Will be interesting to see if/when that happens.