He was not paranoid enough. He was way too lenient with a lot of party members that really ought to have been purged or more thoroughly investigated, because clearly as soon as he died, there was a coup from within the party by all the secret oppositionists who promptly took over the country and smeared him for literal decades.
Ask Lemmygrad
A place to ask questions of Lemmygrad's best and brightest
the USSR did get invaded by Nazi germany, there was a legit dissident faction within the party and ultimately Stalin died mysteriously and got smeared by his succesor. Afaik, a paranoid is someone that ultimately prepares for things that don't happen and most things Stalin prepared for happened.
There was a general culture of normalization of excessive violence due to the 2 world wars and one civil war they just had to endure plus the lasting legacy of the brutality of the Tsardom.
Stalin himself though, the characterization of him as being paranoid is false, people usually point to the doctors plot as evidence of this but if you read into what Stalin actually did and said during this, he kept throwing doubt on the investigation due to a lack of evidence, he was actually a moderating voice - not paranoid.
Here is a little trick for you. If the US govt/orgs they back say a bad thing about a communist its either A. Not even slightly true, or B. Extremely exaggerated, and made to sound worse then it was/is.
Stalin was based af btw.
this is not to say no communist has done shitty stuff. just that theyll always blow it way out of proportion.