[mbell]

You're largely ignoring the primary differentiator in these machines, the power class of the CPU/GPU.

If you use the base model in each category, set all the machines at 256GB disk and 16GB of ram and use geekbench cpu numbers as a performance metric, you get the table below. Also geekebench is a pretty short test, I would guess that the core-m / y-series models will fall further behind under sustained loads. I don't think this is a particularly bad spread of options.

  2017 Macbook                  - 1.2Ghz dual, 3.0Ghz T  - $1499   GBS:3740 GBM:6835

  2018 Macbook Air*             - 1.6Ghz dual, 3.6Ghz T  - $1599   GBS:4189 GBM:7896

  2017 Macbook Pro 13 (non-TB)  - 2.3Ghz dual, 3.6Ghz T  - $1699   GBS:4333 GBM:9440

  2018 Macbook Pro 13 (TB-quad) - 2.3Ghz quad, 3.6Ghz T  - $1999   GBS:4643 GBM:16540

[*] For the 2018 Macbook Air I'm using geekbench numbers for the higher end 7th gen Y-series CPU as I can't find any benchmarks for the i5-8210Y so this should be considered an estimate.