the USSR was socialist trying to impress the world
but really they were failing for a really long time because their main way of being socialist was by having an isolated economy
In fact their economy grew fastest while it had autarkic policies... It began to stagnate in the 1970's and began to import a lot of things. There are several reasons why, the main one their military spending being gigantic compared to their total production (like North Korea today compared to the west), and later Saudi Arabia increasing oil production, making oil prices fall sharply and ruining the USSR balance of payments. World War 2 is also worth mentioning and the fact that despite much bigger destruction, the east got no help compared to the west from the intact USA.
With that said, no, having an isolated economy doesn't make it better, and surely the USSR's economy would've done much better if it could've cooperated with an industrialized socialist west rather than being undermined by and protecting itself against it.
And having an autarkic economy reduces interdependence. It's more of a necessity from international politics than an economic policy.