This type of sighting system is an offshoot of the "run and gun" type shooting games. How many times is such an aberration really useful in real life shooting?
If the target is close enough for this to be useful, just point the barrel and shoot.
You're talking about two different, but valid things here.
In a two-gun or three-gun competition, this is useful. Aiming down the barrel without sights will not give you the accuracy needed to get the par points on the target.
The drawback with 45 degree sights is you can't use them when shooting from your weak side. Courses should be setup to practice that.
In a defend your life situation, they may be put in play as a BUIS when your optic is smashed or muddy, or otherwise opaque. You still may need to make 100+ yard shots. You need sights.
Again, the drawback with 45 degree sights is you can't use them on the weak side and you may need to.
Everything is a compromise.