Clubs set out the season with different objectives. While one team may try to avoid relegation, another may want to win the league. But if both of those objectives are met by the respective clubs then it's a success for both.
For this reason I personally believe we could have a better season, because of our original aims. We set out for a CL spot and are still competing for that.
You set out to win/compete for the league. You did. United fans couldn't hold in their excitement when the signings of Pogba and Zlatan were announced in their triple figure million Black Friday esque shopping spree. And you got Mourinho too, the quick fix, instant success, always wins the league in the second season manager.
On top of that you had a good start to the season so there was double optimism. Halfway through however things started to falter, and you had to re-evaluate your aims, convincing yourselves that after the debacle of LvG a CL spot always should have been the objective and it was silly to think you could win the league straight away.
Yes you've won a League Cup and may even add a Europa league to that too. But at the end of the day had I told you (if this happens by the way) you'll end up 6th with a League cup and Europa League you'd of been a bit surprised considering the money spent and manager brought in. Although maybe you could of been convinced to accept it because of the Europa league. I don't know you tell me
However, if you told me we'd be knocked out of all the cups but end up 4th. I'd be happy. (Cups would have been a bonus but hey, 4th was always the aim).