Also, it feels like we are 1 seamer short. If by any chance 1 seamer gets injured or becomes unfit, the team combination will suffer but I guess they are assuming that UAE will offer a slow surface and spin will play a major part.
Why is Jadeja in the squad?
You answered your question yourself. They are probably expecting spin to play a major role in the tournament which is why they added him to the squad. He is also one of the OGs these days along with Rohit and Kohli which is another reason for his selection.
The dude ain't as consistent as before, but he is still a useful asset in critical matches which is why I am happy to see him in the lineup.