Ehhh.... "In love with" is a bit strong. Remember, that was coming from, what, a sixteen year old girl?
I think the only true mistake on the part of the writers was how they played that final moment between Ted and Robin. The blue french horn bit. I think it was a misstep to have a reunion between two much older adults, one now widowed and in his 50s, essentially mirror an attempt to woo a girl that he made in his 20s. That I didn't like so much, but the rest... I dunno. It kind of makes sense to me. These aren't the same 20/30 somethings that could never make it work, that were never on the same level. These are now adults in their late 40/early 50s. They're in a new stage of their lives. The way I look at it, it's not a "By Golly, she's right, I AM IN LOVE WITH HER! Robin!!! I think I love you, lets get married and you can be the stepmother to my kids and we can live happily ever after together!!!!" It's more of a "Hey, I don't know where this is going to go, but... I don't know, maybe it'd be fun to hang out with her again, just the two of us. Like old times." It showed so much of how all their lives were changing over the course of this finale, one of the big ones to me felt like it was a lack of Robin. They all went in mostly different directions over the years, and only kept in touch for the big stuff. It makes sense to me, that after all these years, after the loss of his wife and a fairly lengthy gap of time without her, he just kind of wants to reconnect and have Robin be a part of his life again. It's not a "I'm in love with you! I've always been in love with you!!!". It's not a "Haaaaave you met me? Alright, lets have sex now."
It's a "Hey, we haven't done anything just the two of us lately. I guess I'll see if I can get a laugh out of her with this thing (the blue french horn)." I don't see it as some massive betrayal towards the Mother at all, or Barney for what it's worth. There's nothing about Barney and Robin's marriage falling apart after three years that surprises me. It happens, and with those two characters in particular, it's not a huge shock that it happened. But it's not like Ted heard about the divorce and "Holy ****, they're breaking up for real, get me in there.... awww ****, I've got this wife and kid as a weight around my neck, dragging me to the bottom." He loved The Mother. He was in love with her. Eventually making an attempt to reunite with Robin doesn't negate that at all. I mean, did we just completely forget "How the Mother Met Me"? She was totally in love with Max, and spent the better part of eight years shutting herself off from romance. With the kind of man we know Ted Mosby to be, I don't for a second believe he would've behave any differently. It's not like he was twiddling his thumbs for six years thinking "How can I make this work for me? How can I end up with Robin?" He's not Barney. I think the story he's been telling the kids is a classic case of Ted's heart and Ted's brain never quite moving at the same speed. Ted's brain might have thought it would be fun to tell his kids about his late twenties/thirties and how he eventually met their mom, but I think his heart was acknowledging that after six years, he didn't want to be alone anymore. The Mother wouldn't have wanted him to be alone anymore. And instead of doing the whole dating scene that he suffered through and eventually became fed up with ALL over again, yes, his first thought is Robin. Sketchy? Maybe. Malicious? Not so much.
And then lets not forget the format of this series. This story of how he met their mother has really been more about growing up with these friends of his, and a TREMENDOUS amount of it has been about his relationship with Robin, whereas the Mother has factored in very little. I'm not necessarily saying it's right, but they've been laying down those breadcrumbs that maybe this story was more about him airing his feelings/reminiscing about his relationship with Robin than anything.
Listen, the execution.... alright, there were some issues there, but I don't take any offense to the intent behind it. I think they could've stuck the landing a little more if they had a bit more time. It was like we were seeing the edited down version of something better. There were story beats that should've been explored and moments that they could've let breathe a little more, and they would've been much better off for it, but their objective here... I'm at peace with it. I don't LOVE it. But it makes sense to me.
I don't know, for all I know this stream of consciousness bit of posting from me has been practically unintelligible, but that's how I feel at the moment. I'm gonna sleep on it.