I think this is the problem with the blue French horn. Ted shouldn't have showed up at her apartment with a French horn. He should've thought about it, but ultimately just called Robin. That would've shown growth. That would've created a lot less ambiguity as to whether Ted was in love with Robin, on some level, throughout his marriage. It would've signified that Ted is no longer obsessed with finding love...no longer defining himself by who he is with (which is something he has done throughout the show from Karen to Zoey to Robin to Victoria).
Instead, it is just Ted, now an adult rather than a 20-something kid, content with who he is, wanting to spend some time with someone who was at one point very dear to him and see where it goes. No pressure. No need to say, "I love you," on the first date. Ted, no longer needs to find the one because he already has and Robin who has never been interested in finding the one can just enjoy her relationship with Ted for what it is. It wouldn't be so grand, it would just be two adults enjoying one another's company at a different stage in life.
I feel like that is where Carter and Bays were trying to go, in which case it is a great ****ing arc for Ted. But I feel like the blue horn kinda undermines that. Instead, it is just another grand romantic gesture that says, "OMGZ! I'M STILL IN LOVE WITH ROBIN!"
I think that is why I am having so much difficulty with the ending. I think a more subtle approach, to the same ultimate ending, would've made a word of difference.
That being said, the ending is not nearly as terrible as some are acting. The ending, in a way, perfectly completes Ted's story arc. But it also does not do so in a perfect manner (or anywhere close to it). So I disagree that the show "outgrew," its ending. It is still the logical end point for Ted. But the show failed to conclude the arc as effectively as it could.