Knowing that I can't trust another player to launch a skill shot attack on target is valuable info - it changes the dynamic of how you'd play with that person.
I totally understand where you're coming from.
However, there exist people who play MOBAS who are easily frustrated and -emotionally- twelve years old. Hiding the rank and ping of all players gives such people two fewer things to get angry or upset about. If they're not angry or upset, they might just either play well and win the game, or -barring that- be a pleasant person to play with. :)
> Knowing that I can't trust another player to launch a skill shot attack on target [because of high ping] is valuable info...
Back in the day, I used to play Descent and Descent 2 [0] over both a 28.8 and -later- a 56k analog modem. My ping times varied from 300ms to 700ms. There were a few weapons in that game that were -effectively- skill shots and tricky to land, but -if you were aware of your ping, and your opponent's likely motion-, landing the shots was totally doable.
In short, just because your teammate is a HPB doesn't mean that he can't cope with that ping. He might always play with that ping, and -thus- be completely accustomed to it.
[0] Both games are 3D, 6DoF shooters.
With LoL being as team-based as it is, knowing if/when my Blitzcrank is going to be able to land his rocket grab lets me know when to launch my ultimate and the rest of the team to join the fight. Having a high ping guy initiate a teamfight is.. unwise.
But quite honestly, I don't believe that hypothesis. If someone is going to get bothered to the point of toxicity by ping, something that is almost completely out of the player's control, they're going to get just as bothered being killed by Malzahar's global ultimate, someone picking the wrong team composition, not getting the lane they want, someone speaking a language other than perfect english, and so on.
It's like instead of optimizing for players to be able to play their best and give them the tools to do so, they optimize for, and drag everyone else down to the level of the emotional child. As someone who is not an emotional child (at least I think not): that's disheartening.
I also don't believe Riot is serious about dealing with the problem - it takes a long history of being a serious jerk before the bans start getting trotted out (talk of "correction cards" aside).
And it makes sense why - banned people don't buy champions and skins.
