Personally coming for the road I prefer the 2 x system. I like have the closer range and the ability to have a cadence that I am more comfortable at. I understand the benefits of a 1x system but I was never in a situation yet where its benefits out weigh a 2x system. However if and when that situation out come up I bet I would wish I had it.
Last year I actually used both 650 and 700c on our Cervelo bikes. If I was doing a standard gravel race I would use the 700c wheels. I believe they are a bit faster and carry more momentum. Also being larger tend to roll over objects easier.
However I used the 650b with wider tires often. I found it be really comfortable. I didn’t feel noticeable slower on them. I. could also take it over rougher terrain, like a mountain bike. I found this to be really enjoyable.
Whether you use 650b or 700c can come down to course or type of riding. I think it is good to have both options. I never thought I would use the 650b wheels once I got 700c but I found myself going back often.