What I like about the RX100M7 is the convenience. It’s got pretty much everything that the A7III has, but in a smaller package, and you don’t have to change lenses. As far as the lens being “slow,” f/2.8 isn’t particularly slow, and f/4.5 isn’t bad either, as the M7 handles higher ISO settings well. Consider that Sony’s interchangeable lenses, for the most part, are f/3.5 at the best unless you want to spend mega bucks on their high end lenses.

As far as flash goes, I wonder if it’s possible to use a flash mounted on an L-bracket, and plugged into the charge port on the side of the RX100. That idea just came to me, so I haven’t had a chance to research that yet. It’s a novel concept, though.

By the way, I’ve done some comparisons between the M6 and the M7, and I don’t see a whole lot of difference between the two. The price on the M7 has gone up $100.00, so there is now a $200.00 difference, and were I to be buying one now, I’d opt for the savings and get the M6. Some of the upgrades to the M7 may not even be useful to the average guy who doesn’t sell their photos or compete in shows. I don’t regret getting the M7, but if I were to do it again, I’d get the M6. Both are amazing cameras, and the M6 has a better rear screen display. Don’t know why Sony didn’t put the same screen on the M7. I think they dropped the ball in that regard.

When I go on vacation I only take a Sony HX99 and the Sony RX100 M2. The Sony RX100 M2 is my favorite RX camera for one reason only, I can mount a SONY HVL-F60M flash unit on it. I can turn the head so it aims up and behind me for beautiful flash results.
The RX100 II is the only RX 100 model that offers a flash shoe.
Yes the new RX100 has a 24-200 lens, but you already have the RX10M4 for reach, what you need is a SONY HVL-F60M flash unit for your RX100 II. If you get one, private message me and I will give you some things you can do to up your flash game.
Good luck and keep on shooting until the end.