If Chelsea is really a weak team, they shouldn't have made it to the quarter-finals. I know that Madrid are the favourites, but not all the favorites can win all the games and win the title. I'm not going to compare the achievements of each team, but their performances on the pitch are valid evidence even if everyone has assumptions and tries to argue in other ways.
No one can say Chelsea is a weak team. Chelsea is always a big and strong team although they are difficult playing at their best form lately.
Sure, Chelsea won't reach the current stage/round if they are a weak team. Don't forget that Chelsea is the leader of group E on the group stage. It proves that Chelsea is a strong team.
However, if we compare the squad quality and coach quality, Real Madrid is still better than Chelsea. Real Madrid also has a better experience and achievements in UCL. I never underestimate Chelsea squad, but I'm sure that Real Madrid will have a bigger chance to qualify for the next round. I even predict that Real Madrid will play in the final round.