Sounds like you hopped intp p7n for the first time, got tripped by a couple of mechanics as expected because that is how first runs of normal raids go and now you're frustrated because you don't know what happened.
Running it a few more times helps identifying issues but the only things on p7n that are guaranteed to OHKO you are the knockback from birds & after Bough cast and if you stood in the area that's about to vanish and... quite obviously markes as a gigantic nope-zone. A lot of other things can be face-tanked, like taking 1-2 exaflare ticks, eating the cow pointblank, letting a tower blow up, getting a Bough into your face etc.
That's not a lot and the tells aren't exactly obscure either; normal raids are known for having very few, if any OHKO mechanics and are designed to be very forgiving. Recognizing some tells quick enough to dodge reliably takes more than a run though, it's part of learning a fight.