Ah, I see what you did there, you changed the date by two months to fit your scenario. That must have taken some work. Of course, if you wanted to come back a day or two or three earlier from BKK, you're out of luck. No flights. And while you're earning the sign-up bonus, if Delta changes their policies or pricing, you get to visit Atlanta instead.
Meanwhile, with flexible currency like Chase UR, Amex MR, or Capital One Miles, you could fly when you want and you wouldn't be subject to the whims of just one airline. You could fly Delta or Thailand or EVA or Sun or Korean, and more. And you could even fly on the original date, that you mistakenly chose. You can't do that with Delta miles.
And what the hell is "miles-per-points?" I've been pretty serious about this for seven years and I never heard of that one.