Ranked new champs: time + mastery
Disclaimer: this post is not a rant. It is an attempt at a feasible solution to a real issue.
Opening day new champs are the bane of fun in ranked. There are 3 main issues: undiscovered bugs, inexperience facing a champ, and inexperience using a champ (aka practicing in ranked). The first issue genuinely ruins games, but is usually at least countered swiftly with champion pick disables. The second issue is really a non-issue. It is no different than facing a rare our non-meta pick.
The prevailing issue then is, I think, effective 4v5 matches where someone picks a champ hoping to win the match due to OP release day syndrome, but basically feeding and costing his team the match because that player doesn't know wtf he's doing or how to work with the other champs in a team comp. However, riot does not want to have a tiered release where a champ is first in normals and then in ranked. Therefore, I suggest a time vs mastery system.
Basically it works as follows: when a champion is released, for 48 hours thereafter, a player must have level 3 mastery to use that champion in ranked games. That mastery requirement reduces by 1 every 36 hours after, so that after 5 days, the champion only needs level 1 mastery to use in ranked. On the 7th day, it will be available the same as any other champion.
Why is this better than a tiered release? Well first, a tiered release isn't going to happen. Second, this means that when you see the champion in a ranked match on the first day, the player will have already performed well enough with that champion to have earned rank 3. Third, this means that people using the champion at the end of the week will have at least been able to, theoretically, see the champion used effectively so they'll have some base strategy to go on. That way, teammates need not dodge when the champ is picked on their team.