But it doesn't make someone with 300 XP given to them over the course of the campaign able to learn MORE than any other person who has 300 XP given to them over the course of the campaign.
In a system with career skills vs non-career skills, that cost different amounts of XP, one player who spends 300xp could very well have more talents and skills than someone else who spent 300xp.
Make two characters with my house rule with the same end goal and make the one who takes skills first gain more things with less experience. Until you do that, you haven't proven me wrong.
My assessment:
RAW: Order of purchase is important, specializations should always be purchased before skills within those specializations, unless you aren't going to ever take the specialization. A person who buys skills before specializations will progress slower than someone who buys specializations before skills.
My house rule: Order of purchase unimportant, but does not make a person who chooses to buy skills before specializations have the ability to progress FASTER than someone who buys specializations before skills.
This is what I mean by the discount not letting anyone progress faster than RAW. I'm saying someone who buys skills before specializations WILL NOT progress faster than someone who bought everything optimally.