I’d say teams with both Cripps & Rowell generally only have 1 super premium - because they are often trying to squeeze Neale, Berry, JHF, Daicos & Ward/Stephens on field as well.
I mean Cripps and Rowell cost the same or less than the top 4 premium mids and a rookie. Point stands that it's realistically 2 of the 3, or equivalent elsewhere, and those 2 vs the 3 and a cheap rookie. If you want to spend your 700k on Gawn then do that instead but for simplicity of comparison it's easier to keep the two constants and only change the moving pieces.
Doing things in isolation and removing variables lets you actually do the "x vs y" and see if that idea is worth continuing on with. a, b, c and d are just noise that distracts from the variables that you started with.
It is a valid point to mention that elevating a base price rookie up to Rowell is likely going to push a Ward/Stephens out of the starting line up, so you should use whatever your projection for them is, I used 65 there because that's upper end of my ballpark, your usage may vary, as the replacement value (you weren't fielding the 123k guy after all).
FWIW, I've currently got Stephens at M11 in my side, although technically I'd say Rachele is the M11 if I was ranking them on expected scoring.