So, is smurfing reportable?

sadly, no, it isn't.

there is no way to absolutely prove that it is a smurf. Riot allows smurf, probably unofficially. Every pro player has one to try new stuff on. You watch a twitch stream, all of them have smurf accounts that they will switch between on their stream. There is no way to do away with them.

No

{quoted}

Like, when someone is very obviously smurfing -- is that reportable?

Also it is not a Problem unless you are Platinum. Diamond+ Smurfs will usually win all their Placements games and end up in Plat+. However in Plat I always gets them during my promos in the opponents Team. Seems like a curse.

Isnt, never was and never will be.

no it isn't