Bathroom (horizontal) venting question

[Hard Rock Homes]

I have a 21'x6' bathroom with fixtures all along one wall. All fixtures were vented right behind the fixtures with the vents inside the wall running upward. The sink is wet vented. It looks like the plumber ran a horizontal vent in the attic, receiving the fixture vents from below, before exiting out the roof. I've seen different advice on here about this ranging from "a horizontal vent is never allowed" to "it's ok if it's 42" or over the highest fixture" to "it depends on the distance" to "as long as it's sloped to allow the condensate to run down". This horizontal vent line is slightly sloped back to the drains, but it's very slightly sloped - no where near 1/4" per foot. Maybe possibly 3" slope over 16-17 feet? So I wanted to give a diagram before the inspector comes out. This is a new construction project. Is the below diagram legal?

Edit: trying to post the image failed. Here is a link to the diagram: https://ibb.co/F8PDpVY

 

[Terry]

2" will vent a bathroom group.
The horizontal vent in the attic will be fine with that slope. Nothing in the drawing shows how things were actually plumbed other than the fact that they indeed did have vents into the attic.