I bought a Sl-2 when it first came out just to try it. I liked it so much I traded my Leica SL for a second body and added a grip to it. To me it is the perfect camera, and it is hard for me to imagine any new model or system that would make me give them up. I have moved on to using adapted Zeiss ZE lenses, mainly Milvus and some Classic. I have gone back to manual focusing for the bulk of the work I do. I still have my SL zooms, the 50 1.4 Summilux, and the 35 and 75 APO Summicrons. If I need AF then I will use them. Otherwise it is the Zeiss that I really enjoy.
These tend to be heavy lenses. Therefore having a larger body with some weight is a asset.
Coming from DSLR's I never thought the S1-R was a large camera. It just suits my hands well. The buttons work well for me. I can see at a glance before turning on how the camera is set up. The flip out display is brilliant and I could not see using a camera without it. This would rule out the SL2.
In my opinion the electronics in the Lumix all seem to work better than in the SL. Flash for Godox has always worked with the Panasonic protocol. With the SL- SL2, until just recently, users were limited to inadequate and pricey rebranded flashes.
The body is rugged and the finish durable whereas my old SL scratched easily. I have dropped the S1-r and abused it but with no ill effect.
In my opinion it is a professional grade camera. Some people criticize the number of buttons yet once set up, you rarely have to access them. The layout and options available make for faster shooting. This includes night shooting and when wearing gloves. My feeling is that the designers spent a lot of time incorporating into the system the features that pros might need. Some options lead to faster battery drain, such as constant auto focus. I have never used it. I have always thought the battery life was very good and in fact since it is larger, I expect better than the SL2 battery life
The one negative that users keep talking about is the lacklustre performance when shooting AFC. This may be true. I cannot comment on this because I never use that mode. When using the Leica lenses the AF focus is quick and very accurate. Could not ask for anything better IMO.
The bottom line is I really enjoy using these bodies and rarely do I ever take out my older M 261, Q-P, or S 006 cameras.