It'd be similar to how players wanted to just select their highest unlocked difficulty rather than build up their rift keys.
For better or worse, the way they intend to design CMs now is the safer way to go; this way if players are dissatisfied with how long it takes to build up, they can tune things appropriately and eventually unlock the ability to choose levels.
If choosing levels brings about some sort of unintended consequence (tuning is too easy for example), Blizzard may take that away. That'd probably have a worse impact.
You're right with your concerns, but I also see Blizzard wanting to be careful. This is a new endgame paradigm being brought in, after all.