^This is true. Ted seems to work only as a foil for the other characters lately. And frankly, compared to them, he's really not that interesting.
It's like Ross and Rachel in Friends. The early seasons were all about them, but the focus shifted in later seasons to Chandler, Joey and Monica. HIMYM doesn't really have that luxury, but Ted's part in the story seems to be the least important lately.
That's true for at least 1-2 seasons.. somewhere they missed the exit and the main storyline of how Ted met the mother of his kids got stale and uninteresting. No relationship Ted had was ever going to last because we knew she wasn't the mother so there was never any tension.
Back in season 1 and 2 it was a novelty when Ted met Robin and they hit it off in the pilot episode only for the surprising reveal that she was "just" aunt Robin to the kids but it was nicely written and even during their relationship in season 2 it was still funny.
Yet somehow the show has gotten stale.. from time to time it is still very funny or has some engaging storylines (last ones were the death of Marshall's dad or the drama between Robin and Barney recently).
However i only watch the show out of habit now and that's not a good sign.