It ignores a whole lot more than that. For instance, are we seriously going to pretend that the threat landscape in the Windows 98 and XP eras was anything like what it is today?

Well, I'm not. If he wants to daily drive Windows 98 because it had fewer documented RCE vulns, godspeed to him---and he probably will be more secure, just by virtue of good ol' security through obscurity---but that is not a reasonable solution for 99.999howevermanyninesyouwant% of computer users today.