The point is that it would make the game more fun always. Sure, casual players would be essentially forced to learn more ... what else is aram for other than just fun?
I'm saying that, regardless of whether it's a net positive change, enabling all champs is not a strictly positive change. Partly because of casuals who don't want to learn new champs. Additionally, it'd also make IP essentially useless for ARAM-only players, which invalidates a major form of account progression in League.
Moderate improvement in balance? Really? You are kidding right?
Not all champs in the same role are equally powerful/impactful (e.g. Bard vs. Sona). I will admit I might've been overly cautious in terms of potential benefit.
Again, casual player ... why are they there? To learn. Your 1st and 3rd point are exactly the same.
No, competitive players would be there to learn. Casual players just want to goof around and have fun.
In all cases, you are arguing that casual players are what matter the most.
How did you come to that conclusion? Only my first point focused on the negative impact on casuals. The other two points were about how the proposed change would be bad for all players, both casual and competitive.
In every other instance of LOL, it is the top-level that determine how the game is to be played. Seems silly that everywhere else you'd argue for high level to determine the gameplay, but not aram.
There's a significant difference between ARAM and the other permanent game modes: separate queues. For every other permanent mode in League, there's (at least) one casual queue (i.e. Blind Pick) and one competitive queue (i.e. Ranked). Changes to champ select for competitive players have no impact on casual players. However, in ARAM, both casual and competitive players share the same queue. As such, any potential champ select changes must keep both sides in mind.
Naturally, the ideal solution would be to add a competitive queue for the competitive players. With separate queues, it's possible to tailor an experience for a specific side, rather than having to struggle with the current "One size fits all" approach.