I have both the a7iii & a6600
TBH, I haven't used either for tracking.
A lot of photographers are not all that keen on the a6600 size and design but I've never had a problem with it or my previous a6300.
I have a SmallRig L Bracket fitted and not only is it Arca Swiss compatible, it also improves handling.
I use the a6600 mainly for wildlife and also for travel when out for a cycle or a weekend away in the motorhome.
I tend to use it more than my a7iii kit.
I paid just under £900 for mines from E-Infinity but they are now asking for just over £1k which still makes it a good buy.
Its great with the Sony 70-350G lens, another good lens at a reasonable price. Even huge crops look more than acceptable considering its only a 24mp sensor.
The button layout and menu system will be totally different to your Canon's
The menu system takes a bit of getting used to but not any more than if you moved to another brand.
All in All, I would highly recommend it.
You can see examples on my Flickr photostream