I Got bored so i decided to go back and do some REAL MATH on this.
let's assume every % point is 1 unit for the sake of this illustration. Going by amazon japan current yen prices and we will assume that both units get 10% margins (which was your supposition)
M50 - 64,050 Yen x 18.2 units = 1,165,710 and profit: 116,571
A7 III - 221,000 Yen x 3.5 units = 773,500 and profit 77,350
So going by some basic math seems like Canon's making more profit on the M50's than Sony is on the A7 III's at least in Japan.
Both the M50 and the A7 III's are sold with different kit options,etc as well, for the sake of this I just cancelled all that out as equal.