Rain ? No problem IF pitched correctly.
The Tarptents are designed to be pitched TAUT ( well, most tent are...) , when you see a limp one that is either user error or very uneven ground.
This is a shot from Nepal. That night we got buckets of rain , the field next to us (a dry rice paddy) flooded.
I woke up dry not a drop of rain inside.
Note that I use a rear mid pole to keep the middle of the rear up a bit and to give it (with the front guyline) some good longitudinal tension (same as with A frame tents).