It's perhaps too specific to ask if Lenin thought central planning was flawed. You see, at the time of the Revolution in 1917, not a single revolutionary leader believed Communism could work if isolated within a single country. That idea ('Socialism in one Country') was defined much later in 1924 by Stalin and Bukharin.

Lenin, Trotsky, etc, intended for the Russian Revolution to be the spark which ignited a revolutionary fire across Europe and the Americas. They understood, like Marx, that the capitalist system is highly innovative and productive; just that it also can produce horrendous inequality and suffering. As such, they didn't think a state managed economy could compete over the long term.

According to John Reed's 1919 eyewitness account of the Revolution: 'Ten Days Which Shook the World', in 1918 Trotsky said:

"Either the Russian Revolution will create a revolutionary movement in Europe, or the European powers will crush the Russian Revolution."

It then shouldn't be much of a surprise that Lenin proposed the NEP in 1921, after the German Revolution was crushed in 1919, and hope of revolution elsewhere died. This left the question of how the revolutionary state could catch up. Lenin saw the only remaining possibility as the utilisation of capitalism in the context of state control of industry - this time for profit. And he imagined this as a transition which would last a few decades.

Of course, Stalin had other ideas. The question of why is somewhat complicated, but the gist is that he, like Trotsky, was concerned that the revolutionary state would fail if it didn't catch up fast enough. In 1931 he said:

"We are fifty or a hundred years behind the advanced countries. We must make good this distance in ten years. Either we do it, or they will crush us."

In 1945, while discussing business with Yugoslavian Communists (as recalled in Milovan Djilas' book 'Conversations with Stalin'), Stalin remarked that as the Second World War ended, Communists had to start planning for the next war, which had to occur no more than twenty years in the future. This aggressiveness must be understood in the context of fear.

It's also important to contextualise this history with the fact that actually, initial expectations of what Communism needed to do were pretty low. The Bolshevik slogan of 1917 was 'Peace, Land, Bread'. At the time, Imperial society was falling apart, because the empire was grossly unprepared for the war with Germany. This led to a total system failure, where people who already had very little were going hungry, not to mention the death toll of a war nobody believed in. The empire's private economy had descended into profiteering and shortages of basic necessities. It's unsurprising then that socialism became popular, because for most people the old system wasn't working.

In 1920 Lenin said (source here from Marxists.org):

"Communism is Soviet power plus the electrification of the whole country, since industry cannot be developed without electrification. This is a long-term task which will take at least ten years to accomplish, provided a great number of technical experts are drawn into the work."

To conclude, the Bolsheviks from the start needed a global revolution, which didn't happen. This forced them to consider other options, which could harness capitalist forces without the exploitation of workers, in order to catch up with hostile neighbours. The idea that socialism could exist independently in one state was invented years later. Essentially, yes, the Bolshevik leadership of 1917 knew the limits of a planned economy, and so they never wanted Russia to become a lone revolutionary state in the first place. This ties into Marx's recognition of the productivity of capitalism, just that in the industrial era this efficiency came at a high human cost with unfair distribution of reward. And that was what the Bolshevik leadership had to struggle with, leading to the compromise of Lenin's NEP.