Alternative systems such as...? I can think of several, but none I'd describe as 'successful'.

It's kind of a red flag (no pun intended) when your preferred system can be destabilized with some money stuffed in the right pockets, isn't it? Most failed systems that were 'undermined by capitalists' mostly involved funding and support, not invasion or anything. Meanwhile, democracy and capitalism emerged in the midst of hostile aristocracy and royalty, and survived decades of attempts by the USSR (and now Russia) to undermine it.

My personal opinion is that those systems were doomed from conception, though I don't deny that the US certainly engaged in speeding their demise.

Anyway, that's all beside the point. Both populations and consumption increased under the Soviets, and any other system you care to name, proportionate to their effectiveness at keeping people fed and healthy.