First of all, thank you for writing the trip report! I havent finished reading yet but just need to reply on this.
I usually pay less than 500 baht taking taxi from bkk airport, even less if its from DMK. At late night, many taxi want a flat rate of 500 or 600 if its a big van type taxi that can fit more luggage and pax.
Compare that to what you pay for grab, seems like u pay more. Anyway, just wanted to point out the comparison. I understand you also wanted to use CC, so grab maybe more convenient.
I used bolt as well, most of the time, its cheaper than grab.
Ok back to reading your report lol