Speaking of which, I realized literally only yesterday what the purpose of the Multiclass XP penalty and Favored Classes was. What it does is to discourage players from dipping one or two levels in a class to collect their front loaded main abilities. Like 2 feats for 2 fighter levels, or 8+Int skill points for 1 rogue level, which you can all put into a single skill if you do it at a later point.
Elves are free to dip wizard, dwarves are free to dip fighter, and halflings are free to dip rogue. Which all seems appropriate to give each race as a whole more character and evoke their niche.
But I have to say, in the good 7 or 8 years that I had been casually hanging around Char Op subforums, I am pretty sure I have never seen anyone even mention that Multiclass XP penalties could be a factor. This was something that was in the rule, everyone saw once and thought it was stupid (because they didn't understood what it was supposed to do?), and immediately became common consensus to completely ignore for the entirety of the game's run.