Lenin, however, didn’t create Marxism-Leninism, and never said anything that deviated from Marx.
He didn’t create it, he created the principles for it, expanding on Marx.
Additionally, the move towards this “mixed-economy” you refer to, and the move closer and closer to capitalism signified a retreat, not a step towards socialism. Lenin says this in multiple speeches and reports.
The New Economic Policy was adopted because, in the spring of 1921, after our experience of direct socialist construction carried on under unprecedentedly difficult conditions, under the conditions of civil war, in which the bourgeoisie compelled us to resort to extremely hard forms of struggle, it became perfectly clear that we could not proceed with our direct socialist construction and that in a number of economic spheres we must retreat to state capitalism. We could not continue with the tactics of direct assault, but had to undertake the very difficult, arduous and unpleasant task of a long siege accompanied by a number of retreats. This is necessary to pave the way for the solution of the economic problem, i. e., that of the economic transition to socialist principles - V.I Lenin
Many of the people targeted were Lenin’s old friends and associates. Many were heroes of the civil war. These were people who were heavily involved in the revolution- people who risked everything to bring about revolution in Russia
It was Yezhov who executed them, he was later executed himself for his crimes. Many of them were committed to Stalin and his ideas for socialist development, for example Lazar Kaganovich, and only a few of them were putchists (Like Trotsky) or traitors. I’d like to see your source for the supposed ‘hundreds of thousands’ killed by these purges.
It is an insult to the socialist system to say that an “opportunistic and traitorous” Stalin would be able to become a “dictator” within it.