Since anything we throw at the case that haven't happened is purely hypothetical then no one can say it isn't the right way to compare the launch aligned by first release date even if in this case it have PS2 Japan only and PS4 on more markets (still wasn't full globe). I even remember a famous thread of the smart 13 vs 49 or something like that comparing Xbox tiered launch versus Sony more spread, and that MS would demolish Sony on those markets and the extra months to other territories wouldn't impact much. And in a way the first couple months both consoles sold very near to one another, and even Xbox had shortages. So assuming that if PS2 was to be released WW at that time would mean much more sales can't be proven.
So since the initial date is all that matters than let's look at a different console for comparison.
July 1983-Aug 1985 (2 year, 1 month) NES shipped 4.33 million
Nov 1990-March 1993 (2 years, 4 months) SNES shipped 21.06 million
Would you say that's a relatively fair comparison?
When the herd loses its way, the shepard must kill the bull that leads them astray.