Small tips to seeing if a dps is in "burst" window or just a part where they're doing more damage that isn't lined up with 120s:
SAM: Meikyo Shisui icon
RPR: glowing red (enshrouded buff)
NIN: as you mentioned, trick attack
SMN: bahamut/phoenix
RDM: when they dive in to melee
BLM: ley lines
BRD: honestly, doesn't matter too much, but Wanderer's Minuet and Army's Paeon.
DNC and MCH and MNK I haven't played so no idea.
The rest should absolutely be lining up with 120s burst phase. If doing savage/Ult, definitely hold cards for Div window. Sometimes you'll hold cards and be able to do Astrodyne > Div > Astrodyne back to back with how the timers work with cards.