Well, to paraphrase Molotov, Lenin was even more harsh than Stalin, particularly to his allies. During the height of the revolution and civil war, if he got a letter from a peasant claiming communist party corruption or malfeasance in an area, he would deputize a university professor and some students to go check it out, and if evidence was found of that corruption or malfeasance to their satisfaction (which had no real legal precedent) they had the discretion to either eject them from the party or, depending on the severity of the offense, just straight up execute them, no trial. Which happened fairly regularly. It was not a case of "We have investigated ourselves and found no wrong doing."

Even if you think the evidence standards were lax in the USSR during Stalin's time (which imo they were basically the same as pretty much everyone else's at the time, they were just far more aggressive at pursuing legal actions against high level party members and generals) at the helm, he still always had trials before executing people, even going as far as trying people in absentia, something that Lenin would have considered a ridiculous liberal facade.

Don't get me wrong, these were harsh people, but in comparison to the consequences that would face them and the millions peasants they led if they failed, I don't think they were unnecessarily harsh.