Lenin’s entire work up to the revolution are in depth about why trotsky is unprincipled. Him being wrong in offhanded comments means fuck all compared to that. His lack of principles made him appealing to many revisionists including those with contradictory views to each other. Trotsky formed several factions over the years, with whatever position he felt like at a given time. Per Lenin

The August bloc—as we said at the time, in August 1912—turned out to be a mere screen for the liquidators. That bloc has fallen asunder. Even its friends in Russia have not been able to stick together. The famous uniters even failed to unite themselves and we got two “August” trends, the Luchist trend (Nasha Zarya and Severnaya Rabochaya Gazeta) and the Trotskyist trend (Borba). Both are waring scraps of the “general and united” August banner which they have torn up, and both are shouting themselves hoarse with cries of “unity”!

What is Borba’s trend? Trotsky wrote a verbose article in Severnaya Rabochaya Gazeta No. 11, explaining this, but the editors of that liquidator newspaper very pointedly re plied that its “physiognomy is still unclear”.

The liquidators do have their own physiognomy, a liberal, not a Marxist one. Anyone familiar with the writings of F. D., L. S., L. M., Yezhov,[3] Potresov and Co. is familiar with this physiognomy.

Trotsky, however, has never had any “physiognomy” at all; the only thing he does have is a habit of changing sides, of skipping from the liberals to the Marxists and back again, of mouthing scraps of catchwords and bombastic parrot phrases.

…Trotsky delivers a long lecture to the seven Duma deputies, headed by Chkheidze, instructing them how to repudiate the “underground” and the Party in a more subtle manner. This amusing lecture clearly points to the further break-up of the Seven. Buryanov has left them. They were unable to see eye to eye in their reply to Plekhanov. They are now oscillating between Dan and Trotsky, while Chkheidze is evidently exercising his diplomatic talents in an effort to paper over the new cracks.

And these near-Party people, who are unable to unite on their own “August” platform, try to deceive the workers with their shouts about “unity”! Vain efforts!

Unity means recognising the “old” and combating those who repudiate it. Unity means rallying the majority of the workers in Russia about decisions which have long been known, and which condemn liquidationism. Unity means that members of the Duma must work in harmony with the will of the majority of the workers, which the six workers’ deputies are doing.

But the liquidators and Trotsky, the Seven and Trotsky, who tore up their own August bloc, who flouted all the decisions of the Party and dissociated themselves from the “underground” as well as from the organised workers, are the worst splitters. Fortunately, the workers have already realised this, and all class-conscious workers are creating their own real unity against the liquidator disruptors of unity.

The Break-Up of the August Bloc (1914)

And again from 1914 we have Lenin writing Disruption of Unity Under Cover of Outcries for Unity which I won’t quote cause the entire thing is about this matter so I would be pasting the entire work. But long story short, he tears into how Trotsky uses claims of unity in order to increase factionalism. His principles are nothing even to himself.

Trotsky’s “unity” was a split by any other name

In the very first words of his resolution Trotsky expressed the full spirit of the worst kind of conciliation, “conciliation” in inverted commas, of a sectarian and philistine conciliation, which deals with the “given persons” and not the given line of policy, the given spirit, the given ideological and political content of Party work.

It is in this that the enormous difference lies between real partyism, which consists in purging the Party of liquidationism and otzovism, and the “conciliation” of Trotsky and Co., which actually renders the most faithful service to the liquidators and otzovists, and is therefore an evil that is all the more dangerous to the Party the more cunningly, artfully and rhetorically it cloaks itself with professedly pro-Party, professedly anti-factional declamations.

https://www.marxists.org/archive/lenin/works/1910/np/ii1.htm#v16pp74-209

So because Lenin was duped by a spy his later analysis of Trotsky is incorrect? What are you even saying?

Here’s some more:

In Adventurism (1914), Lenin places “Trotskyism” among groups representing “sheer adventurism.”

“… Trotsky behaves like a despicable careerist and factionalist of the Ryazanov-and-Co. type[.] Either equality on the editorial board, subordination to the C.C. and no one’s transfer to Paris except Trotsky’s (the scoundrel, he wants to ‘fix up’ the whole rascally crew of Pravda at our expense!)—or a break with this swindler and an exposure of him in the C.O. He pays lip-service to the Party and behaves worse than any other of the factionalists” (Lenin’s Collected Works Vol. 34, pp. 339-400).

“Roland-Hoist, like Rakovsky (have you seen his French pamphlet?), like Trotsky, in my opinion, are all the most harmful ‘Kautskians’, in the sense that all of them in various forms are for unity with the opportunists, all in various forms embellish opportunism, all of them (in various ways) preach eclecticism instead of revolutionary Marxism” (Lenin’s Collected Works Vol. 35, p. 200).

“… it was just as sad to read about the bloc between Trotsky and the Right for the struggle against N. Iv. What a swine this Trotsky is—Left phrases, and a bloc with the Right against the Zimmerwald Left!! He ought to be exposed (by you) if only in a brief letter to Sotsial-Demokrat!” (Ibid., p. 285).