Sorry for the late reply. (Still need to make time to respond to Wrecks thread too.)
Here's my 2 cents, Yoshida will stay on the project as long as he is able too. Clearly the game is a passion of his. However he has openly stated that he will always do what is best for the company and do what they need.
When one of the conditions for accepting a promotion is remaining on your current project I think it's safe to say he does not want to pass on the torch.
Now I fully admit I have not read your blog post yet, so I might just be parroting some of your points right now.
To further elaborate on Kaelwryn above me, think of it as an evolution instead of changing what you are playing.
Gladiator is an interesting case because outside of flash you really don't get any White magic like the traditional Paladin. This might be because the the job fantasy of the PLD was to mix sword mastery with shield mastery. (Also if I am not mistaken the Job is called Knight in the Japaness version.) However self healing and group defensive magic starts to show up heavily from 50-70.
I like to use WAR as the prime example of class to job evolution since I am biased. Where all the base combos are the same with Marauder and WAR abilities gained are the Stances, a few CDs. (Actually as of 4.2's reworks Inner Releaee is an evolved version of Berserk fitting more with the idea of being the base job+) and abilities that spend the resources those stances give you.
TL: DR
Jobs tend to focus on new aspect the base Class lacks.