If on average it is just the one long haul trip then, all things considered, that alone does not justify a switch in my view. I would have thought that a much more important consideration would be the pro's and cons of Delta v AA, assuming the OP travels domestically from time to time....

A note on Amsterdam, I hear it is improved from a few months ago, but make no mistake, it was an absolute disaster zone back in the summer, and I have studiously avoided it ever since in favour of Rotterdam, although I am braving it again in Feb. Never like Paris CDG. As I hardly ever transit though Heathrow, I can't say much about it, though I can well imagine it is a none too pleasant experience.