I don't really get the account sharing. Its a rule that frequently goes unpunished especially if accounts are shared by friends.
Secondly, they've been monitoring the pros through September...do you know where pros have been for most of September? Korea. As in, not their normal region for most players. I think its ridiculous for Riot to expect pros to do anything other than share an account. They have to be in Korea, they have to play games in Korea and they aren't going to level up a brand new account, nor are they going to dust off some old accounts they might have and place in Plat 1 or D1 or where ever is the highest rank they can get. They're going to borrow/buy accounts they can actually get real practice on in solo queue.
I know some pros just do the ranked climb, but I don't think its unexpected to learn that not all of them do. Its not like they were boosting, they were doing it in order to prepare for Worlds. Unless Riot provides appropriate accounts for them--which they might, and if so I rescind most of this statement--I don't think account sharing is an unreasonable occurrence.
That said, punishing for toxic behavior is totally warranted. As a pro its unacceptable to behave in this way. Whether the fines are enough or not remains up for debate. On one hand, I imagine losing Diamondprox, for example, would have been way more devastating for Gambit than most other teams. Gambit wouldn't have gotten as far as they did without him, especially since they had to start from play-in, so losing him in the first game would have possibly prevented them from ever getting a chance to even try for regular Group stage. Conversely, some might say losing Uzi for a few games is more devastating, as the ruling came out so late, a team that lost in Play-ins like Gambit would be unaffected given how late this ruling was announced.
You also have to think about the magnitude of the behavior. These guys aren't saying the N-word on a livestream or something, they are griefing in random solo queue games. The fact is, behavior in a random game is less important than your behavior on-stage. Ranked is more casual, anger is going to happen and its not like most people's careers are on the line. If I or any random person on Boards is toxic, we aren't getting fired or paid less at work. That said, I suppose it isn't unreasonable to expect better behavior out of professionals; the punishment is warranted, its the severity that I'm not sure about.
Like, if Lebron James went to some random pickup match or entered some recreational tournament where he lives and was just a total douchebag to everyone, basically doing the equivalent of griefing in a basketball match...should he be banned from the first few games of the NBA season? Perhaps because a game of League is so much more public and irrevocably attached to the sport that good behavior is more important in this case? Its not an easy answer.
Additionally, Riot also mentions how they took into account recent behavior throughout this season. The players who received fines have already received their warnings at some point. The players who were warned are expected to rethink their behavior and try to improve, or else they receive fines as well. I don't think its unreasonable to think that if they don't improve after the fines, more severe punishment like some of you are suggesting would be appropriate.
For me personally, I have two thoughts. One is I don't want to see players banned from their first few games willy nilly just because of solo queue shenanigans. If they don't improve, if they remain toxic despite the warnings and fines, that's one thing. As a spectator, its really lame to have something as important as Worlds be potentially decided because of a few players' behavior in solo queue. As long as the players improve and continue to conduct themselves civilly on the Worlds stage, I think a fine is an appropriate punishment for the moment.
My other thought is...why did this take so long? If Riot wanted to monitor pros' behavior in preparation for Worlds, why talk about it after Play-ins is basically over? And why were they being monitored through September, why not year round, so that way you can dole out punishment much earlier? Did they just monitor them since they were all in one region? If they banned the toxic players from their first match or so, as many suggest, then this punishment would have literally 0 effect on Diamondprox because this ruling was announced after Gambit was already eliminated. Its just such random timing.