So you are implying that the following scenario is correct..
-Level your glad to 'X' level (quest level, 20/30)
-Pick PLD, level to 50
-Make decision to play DRK instead
By going and completing the DRK quest, are you implying that your DRK would start at class rank 30? or is it at 50 and you are just assigning points?
Personally, I prefer the xi approach of having to physically level the new class. Just making sure I'm following your thought process.