For the type of riding you describe, I find the Domane to be perfect. I have a 2020 SL5. I have ridden a Checkpoint with the same 105 drive train (so an apples to apples comparison) on packed gravel, and found no advantage to the Domane. The Checkpoint's tires are not as good on paved roads/MUPS. If you want to switch to a "gravel" tire, you can go up to 38mm on the Domane as well.
The only proprietary part is the seat post.
The Blendr mounts and Ion/Flare lights provide a very nice integrated look. You don't have to use those, but I really like them.