I don't see those two things as having a relationship with each other. We know Russia wants trump as the president. We also know that they want Sanders to be the nominee. We also know that Republicans are openly telling people to switch their registration to vote in the caucuses for Sanders. People don't receive 'help' like that if they are a strong candidate. That is done when there is manipulation of a process and the weakest candidate is chosen. Russia and the GOP have internally designated Bernie as being the weak link of those running as a Democrat. Why did they?
We don't even know that Russia wants Sanders as the nominee. All we (maybe) know is that they wanted to boost him a little early, when Biden was the frontrunner. For all we know they were just trying to hurt Biden, or make the primaries more divisive.
But let's pretend you're right and the Russians think Sanders is a weak candidate. What the fukk would that matter? Both of our own fukking parties never have the slightest clue who a weak or a strong candidate is, and you think some ESL dudes from a different culture on the other side of the planet are the GOAT American political analysts? Both the Republicans and the Democrats thought that Clinton was the strongest Democrat and Trump was the weakest Republican in 2016, how did that work out?