I'm excited by the potential for improvement next season. I can see so many positions where adding a quality player will make a big difference. If the right 2 or 3 players are added in the right positions, we could easily be 15+ points better off next season.
In my opinion, amongst the top 6, only Man United have the same room for improvement next season. Spurs could theoretically improve every position bar 2 or 3, but it's more likely they lose Alderweireld and possibly Eriksen--and they're neither flowing with cash or an attractive option for good players. Chelsea have a lot of good players already and will do well to hold on to Hazard. Liverpool and City would do very well to improve on what they have, in real terms they're pretty much maxed out points wise in my opinion.
Mustafi out and replaced by a quality centreback, possibly even Holding if he comes back strongly, and then a productive, speedy wide forward instead of Iwobi/Mkhitaryan (both good players in their own way, albeit inconstently) and we would be a much better team straight away.