Qatar's only advantage in this world cup is as the home team, nothing more.
while Senegal, has several players who play in the European league competition. apart from Sadio Mane who became the mascot of their squad, there are several other names who also have important positions in their respective clubs. such as, Edouard Mendy who became the main goalkeeper in the Chelsea team, Kalidou Koulibaly who became this player in the Chelsea defense, and several other names who played in the European league. in terms of strength, it is clear that Senegal has more depth than Ecuador and Qatar. the FIFA rankings are also quite far apart.
Clearly, Senegal's probability is greater as a team that is certain to qualify for the next round than the other two candidates. However, in football it is teamwork that determines a victory. for the Netherlands, I've covered it in many previous posts.
You haven't checked the recent matches involving Qatar, and that is the reason why you are underestimating them. And this is the same team that won the 2019 AFC Asian Cup, by defeating Japan in the final. I know that AFC is not a tough confederation, but they have performed well against various European teams recently as well. One thing I don't like about Qatar is the dominance of naturalized players in their team. A large part of their squad is made up of players who have no real connection to Qatar, but representing them. Bassam Al-Rawi is a prime example.