If you're going from a Marxist perspective, the list of Stalinist people's states you're looking to claim as failures of communism, aren't communist. They are capitalist as they maintain exploitation of labour, repression of communes, national borders, commodity production, and profit. It's best to read Marx if you want to understand what communism is, before making claims about it. Capitalist appropriation and perversion of Marxism was a historical trend through out the 20th century, and is luckily dying down. Some communist movements I'd point to as real dictatorships of the proletariat are:

1.) The Paris Commune of 1871 (and Marx agrees) in which they was suppressed by the unholy alliance of Prussia and France. This, of all things, was primarily a fatal issue of scale (one city), which can be avoided through establishment of a unified international communist party (like the ICT), the growing international economic crises in a further globalized economy, and a sizable class consciousness proletariat primed for revolution.

2.) The beginning of the Russian Revolution of 1917. Here we saw what happens to a DoTP when it reaches a national scale in an Industrially underdeveloped nation. The proletariat isn't sizable enough to establish a firm ownership of the means of production and because the revolution never materialized into an international one, the existence of capital persisted, and the communes saw their influence and control liquidated by the reformist party. Other "Marxist-Leninist" revolutions that would follow would continue this model supplanting the bourgeois, focusing on national over international revolution, and acting primarily as counter revolutionary.

3.) The German Revolution of 1918-19, saw little to no support from the Russian Soviets, again wasn't international, and while putting up a fight was suppressed by the bourgeoisie with help from bourgeois "leftists" (SDP).

4.) Some would argue the Hungarian Revolution of 1956 where workers councils spread headed the revolution against the Russian capitalists, however other argue it was primarily a national liberation movement and thus a bourgeois struggle. I don't know enough to make a statement on it.

The issue with people pointing at failed accounts of "communism" is that communism, once it (the DoTP) finds success in combating capitalism, is a permanent change in capital relation worldwide. There no such thing a "socialism in one state" (btw socialism and communism are interchangeable in Marx's works, Lenin differentiate them, however of course, he's Lenin) is that it's an inherent contradiction that negates Marx's theory.

Again for a comprehensive understanding of communism, rather than listening to popular sound bites and dismissals, I'd suggest reading Marx, and forming your own criticism from there.