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Any elite club that made it to the round of 16, a sign that these clubs have 50/50 chances of either qualifying for next phase or getting eliminated at the end of the competition.
No, some teams have a greater chance of qualifying for the next round if you really do the analysis. Real Madrid, Manchester City, Bayern Munich, Arsenal and PSG have a greater than 50% probability of qualifying for the next round compared to their opponents, so a 50:50 chance does not exist for every team to qualify for the round of 16 this season.
Weaker clubs merely exists in UCL to dash out good points to the competitive elite clubs. The attacking positions paved by Arsenal is brilliant, they're on the next level of upgrading to new edge. Arsenal are balance when it comes to performance, they are still in the UEFA Champions League and that's one of the trending facts concerning Gunners. Mikel Arteta and his players are giving in their very best to secure good points.
Many of the last 16 matches have not been very exciting as it is too easy to find favorites in many of them, but surprises can always be expected in some matches such as Barcelona and Napoli as well as PSG and Real Sociedad. Inter vs Atletico Madrid is one of the most interesting, but Barcelona vs Napoli is also good enough to be considered a great match.
Apart from that, I don't think the favorites are really challenged this season in the round of 16. Real Madrid is very superior to Leipziga, Manchester City is superior to Copenhagen, while Bayern Munich is also the same.