Your point about when pure and shield healers were more defined leading to people picking two of both isn’t really in line with reality because everyone knew double shield healer was an overpowered combo, it would have been the strongest if not for AST’s scaling buffs
Regardless a meta already exists, whether more job variety would lead to a harder meta is up for debate but the meta already exists, if the point of the beige design is to avoid a meta they’ve already failed. Go into a speedrun or ultimate high end prog group and you’ll be laughed out of the party as a WHM or a MCH for example