Is this wiring configuration exceptable or is it considered a defect.
The exposed wire nut connection.
If its low voltage wiring, I wouldn’t address it; I have low voltage excluded in my agreement.
That is pretty typical of low voltage wiring for the irrigation system, I would note that the valves and wiring would benefit from some protection from the weather and mechanical damage, but that’s about the extent of it.
Regards
Gerry