I've compared all three RX10 marks side by side in the store. Yes, 600mm is nice but the Mark III is a big camera. The Mark I and II versions are much more comfortable.
If I know I'm going to need more reach, that's when I'll default to micro four thirds with the 100-300mm zoom (600mm FOV at the long end). But 24-200mm at a constant f/2.8 covers just about everything except wildlife.
The RX10 is a fun, all-around camera. Image quality is very good. I'm continually amazed by what that one-inch sensor can put out. The Mark I version has the same BSI sensor that's in the RX100 II and III. 20mp is enough to allow for some cropping.
Lately, I've been using the RX10 to video my nephew at a number of Cub Scout events (not sports). Things like the Pinewood Derby. As I mentioned above, unless you need 4K, video is outstanding.
The Mark II offers a better EVF, some autofocus improvements and 4K video - but costs nearly twice as much.
Another option in the same price range as the Mark I is the Panasonic FZ1000. It offers a better EVF and a 25-400mm zoom. But the lens is f2.8-4.0 and you give up weather resistance to the RX10.
Overall, I'm quite pleased with the RX10, despite the model being a few years old.