Didn't stop the attack on the Capitol being organized there. In fact there is another attack being organized there for the inauguration. There are many far-right watch groups tracking this.
Perhaps telegram should crack down on these channels during this crisis, yes. Parler made no attempt to turn down the temperature by removing calls for murder, assasination, or civil war.
These platforms are at this moment currently being used to mass hype up an increasingly armed and paranoid segment of the population hyped up on years of cult-like propoganda, conspiracy, and dehumanizing of their imagined enemies. It was a stroke of luck they did not take out Congress the other day, I'm sure some will try again.
If you want a clue where this ends up unabated and exploited, I encourage you to look into the 1994 Rwandan genocide.