i think expecting a tier2 class from only ranking/leveling is to easy, we all know leveling up is given in any MMO asking to get a tier2 class with out any challenge other then getting to r50 is a game for pre-teens. sure a similar systems worked in the passed but making it to easy to achieve will lower the value of achievement.
unlike FFxi where you need any starter job to 30 to have access to any of the advance jobs quest line doesnt seem realistic. but final fantasy tactics needing multiple classes up to a pre-req rank like 20-30 to have access to a quest line would be more ideal in the current system. getting lancer for trick attack getting pugilist for sneak attack getting archer for flee to now have access to a quest line to unlock thief would work in the current system. if you notice not one class has what it is needed to make a classic job.
each class should have its own class only traits and abilities to make them more unique. passive traits that rank up as the class ranks up, and marks should be used for training quest which can give lore and how to properly use "Heavy ...." which can be used with other classes. this should also apply to active abilities each class should have enough class only skills that would some incentive for players to play that class, something similar to FFxi 2hour abilities.
this system would work with the current system with minor tweaking. but each class's "class only" traits and abilities would offer uniqueness. like thief only passives could be evasion up & treasure hunter, while lancer could be parry up & critical rate up, pugilist can be evasion up & base damage up, archer could be evasion up & melee accuracy up... along with class only abilities similar to FFxi's 2hour abilities can give more uniqueness needed in the current system, keeping the flexibility with the mix & matching skills. i just wish weapons was more flexible also with only artifact weapons that would favor some classes over others.
personally i would like to be similar to range physical attack version of a red mage. red mage with pistols that would be so cool. unlike FFxi's red mages had to run up to melee attack if they wanted to contribute with out wasting MP for debuffing/buffing. but that also puts red mage in a dangerous location in battle. a range melee version of a red mage would be more ideal for a jack of trades class