Several points
1. We had an awful pre-season and started poorly as well meaning we played catch up this season leaving is little room for error as well as having only one striker and a new DM to work with. Hopefully our start next season will be less amateur.
2. As you say squad weaknesses, Carroll may be a good player but not in central midfield where we require power and dominance. Next season I am sure we will have competition for Dier and Dembele.
3. Inexperience, youngest team in the league, at times we have been naive, that will change.
4. We still need a proper wide forward like Martial and maybe a Boufal style dribbler, at the moment we have Alli, Eriksen and Lamela who are all number 10's really and sometimes it looks a bit unbalanced. I am sure that will be resolved.
5. EL football, every fan thinks it makes no difference but every manager feels it's a handicap, I believe the managers over the fans. The EL means playing teams we don't care about in places like Kazakstan. It's a hinderence, CL by contrast will fire us up.
Next season I hope our squad will have better balance, more experience and for once a half decent pre-season. I think we will continue to get better, I am shocked we did this well to be honest this season.