Real Sociedad is just a middle team in La Liga. They shouldn't be as strong as PSG, their squad depth is surely not very convincingly. PSG has better players in all lines, in theory PSG must win the match.
However, Real Sociedad performed quite well in UCL this season. They never got a lose in the matches of UCL group stage. They even leads the group D, it is impressive to see their achievement in UCL this season. This is something PSG will have to be wary of, they mustn't underestimate Real Sociedad because they played well in UCL.
I also don't care which team to qualify, both are good teams. But PSG should have a better experience in UCL.
But all of this really only serve as weak indicators of which team is better than the other and would hence go to the next round. We have seen plenty of surprises over all those last few months in all competitions. In the Cups, in the UEFA competitions, in FIFA competitions, in domestic leagues. I could mention plenty of great examples where the current position in the table meant nothing for the outcome of the game.
That's why the second part of what you said is important. Real Sociedad had
by far the best defense in the Champions League and this is impressive. I think this game will be highly interesting and since I like Mbappe, I would wish for him to make it into the next round.
For this reason, nothing is impossible in football, sometimes we are sure the bet in the club is much stronger but in fact lost quite easily. This is sometimes in the prediction based on the statistics of the strength of the team. Regarding Real Sociedad and PSG PU. Statistically, actually PSG should have things that are much stronger both of them compete quite significantly and tightly. And it's true, whoever the winner is, they deserve for this, because sometimes the match at UCL is quite different in the euphoria. Either Mbappe will stay on PSG after the transfer market or not, this will definitely give a significant effect on PSG itself.