My primary uses for my A9iii are shooting sports and events. I also bring it out for a few niche applications. as well. To the OP - RAW files are fine, but if you make a big mistake with underexposing, they are not as malleable as the OG A9.
In the former, if you need 60 or 120FPS, then there is no other choice. But in some sports like cycling which are technically easy to shoot, even an A7iii can do quite well with native glass.
For events, it is very nice to be able to shoot outdoors with a fill flash speedlight at 1/2500-1/4000. I use the Tamron 35-150 as a one lens solution and a Westcott speedlight on the A9iii and it is a super combination that can't really be replicated with any other body on the market.
There are also some really cool niche applications for the A9iii. One is pairing it with the 100GM macro with or without the 1.4TC. Shooting bees in flight handheld suddenly becomes pretty normal and it is easy to do with a surprisingly good hit rate. 60FPS is a real game changer here.
The other niche use I've discovered is shooting really fast, I.e. 1/32000 SS in full daylight. You can turn day into night with a strobe. I suppose you could do it with bulky ND filters and a really powerful strobe, but it is super easy on the A9iii.
I agree, as it was already said here, that it's because A9III is not a completely general purpose camera, contrary to A1 series.
It has some drawbacks:
1) resolution
2) DR
3) some caveats when shooting really fast (or just missing contacts) lenses - this was somewhat alleviated by a firmware upgrade, but you have to accept some pixel-level fringing (or just shoot with slower SS by using a ND filter)
4) flash - while it opens up new possibilities, unless you're using supported Sony native flashes, it is quite tedious to get it to work (setting flash timings manually) from what I've read...
