*If you don't play normals when AR URF is out, that is exactly what I mean by splitting the community. Also, Aram exists by itself for a reason. If you just look at what happened to Dominion, you can see that multiple sub-gamemodes can't efficiently exist. Not to mention that it's pretty obvious that having 3 gamemodes (ranked, norms, aram) doesn't divide the community as much as having 4 total gamemodes (ranked, norms, aram, and now arurf)
*Aram does grow stale and has always been the least popular game mode of the current 3 permanent ones. It only doesn't seem stale to you because you have nothing to compare it to.
*AR URF can have a meta, and we got a glimpse of it's effects in just the weekend it was around when ARAM/ARURF specific accounts dominated. Aram has always had an exploitable meta with ARAM accounts, not sure what you're talkin about there
*Once again, you can't have both Aram and Arurf. We're talking about having a new queue, a greater stress on matchmaking, a new sub-community for Riot to entertain, etc. "If I'm not playing one, I'm playing the other" which is another way to say "If I'm playing one, I'm not playing the other"...aka splitting the community. And you misunderstand the term "cost efficient". Riot has bills to pay to keep their servers/website/gamemodes running. They have employees to pay, advertisements to create, tournaments to run, etc etc. It may be a "free game" but you can still pay money for ig options, and ARURF would simply not provide more revenue than it takes to keep it running. So ya, permanent ARURF would be cost ineffecient for RIOT (which would result in a greater strain on maintaining the main game's functions)