You say that all the parts here should be rated for 15A, but then go on to say the drawing intends to show outlets with 20A sockets. First, not my drawings. Second, why? 15A receptacles are rated for a 20A pass through and OP's drawing doesn't even have a pass through to another potential 20A outlet. By limiting the sockets to 15A, no 20A appliance can be run through a 15A switch, which would be the only potential concern here.

Why do you feel that the wiring should be rated at 15A vs. 20A? There's nothing wrong with wiring using 12 gauge for a 15A or 20A circuit. OP has a 20A circuit, which is wise when both a dishwasher and disposer share a circuit.

Anyone who wants to be confused by (if less than 14 gauge) shouldn't be doing their own wiring. Why would I list the volume requirements for 12 gauge, then go on to say less than 14 gauge isn't counted? People were confused by 1/4lb burgers vs. 1/3lb burgers as well, thinking that 1/4lb was bigger. These aren't the people who should be doing electrical work or ordering my food, even as a DIY.