dondon, you seem to be making the false assumption that increased flexibility is automatically better.
FE13 offers some flexibility, and that flexibility offers a unique set of options to each character. FE11/12 offer more flexibility, and in doing so make the distinctions between characters pitifully tiny. They no longer have mobility or weapon access or dramatic stat differences as inherent qualities: instead, they are nothing more than a jumble of similar stats and growths with some WExp mixed in, and you glue that virtually-identical jumble onto whatever class you wish. It's a disgusting mockery of FE.
In FE13, if you want more options, you have to get those options with different characters, or work around it somehow. Berserker is a fantastic class, offering huge Str and Spd bonuses in Double, but you can only access it by reclassing someone. If you want Vake to be a Berserker, you have to choose whether to promote him to Barbarian immediately at LV10 and go to Berserker from there, spending more time in an unpromoted class, or promote him to Warrior and then go to Berserker after gaining some levels in the promoted class, taking longer but spending more time with higher promoted stats and getting different skills.
Frederick is a highly important character, especially on Lunatic. At LV10+, he's essentially offered a four-way branched promotion - or rather a five-way path, as he doesn't need to use a Change Seal at all. The most obvious options are Paladin and Dragonmaster. Either one will improve his Spd, Res, and mobility to different extents, giving up one of his three weapon types but also at least one of his two weaknesses as a Great Knight, with Dragonmaster in particular giving up both weaknesses in exchange for a weakness to bows. He also has Griffin Knight and General as alternative options. Griffin Knight gives up not only swords but also lances, having a number of stat disadvantages compared to Dragonmaster but having more Spd and soon getting the Carrier skill for even better mobility. General instead gives up mobility to improve Frederick's other stats even more. It also allows him to learn Defense Cry, a team support skill especially valuable on the highest difficulties, when you don't have stats to spare.
Most characters don't have quite as much flexibility readily available. Regardless, a set of 3-4 tiers of branched promotions offers plenty of options for each character, unique options which improve the distinctiveness of each character rather than destroying it.