This will be controversial, but i actually think this is a great change for the game.
For too long have i seen post after post of teambuilder-mains asking for blind pick to be removed so that they can get faster queue times in team builder. it's wrong and this is a good response to all-but prove my responses to such threads have been correct.
You're NOT meant to be a one trick pony spamming the same champion. You're NOT meant to only play one role and get it every game.
Teambuilder exists for a very specific reason: to practice a champion/role that you would like to improve on.
People below level 25 need to improve EVERYWHERE. They have lots to learn in every role. Preventing them from doing teambuilder just prevents them from getting to 30 without ever having played anything other than mid, then going in to ranked and going "mid or feed".
Go play blinds, try new champs and learn the game as a new player. It's a lot easier to learn when you're new than it is to learn a role you never played pre-25 then try it out against a platinum player because you've done well in other roles.