My only doubt concerns the actual effectiveness of such setup, since turrets spin times would maybe not be fast enough to point and shoot to most of incoming ordnance.
They are fast enough to shoot incoming missiles and torpedoes, as my gunner can manually do it and 'target only' can take them out too.
The problem is that we cannot target a second incoming torpedo as quickly as point defence does. If we had the ability to target multiple targets, if torpedoes/missiles counted as 'hostile', if there wasn't a delay on the sensor using 'target highest threat' as the previous highest threat registered as destroyed, or if there was a simple means to 'cycle incoming missiles' in our targeting array, there would be no issue.
If you've got two torpedoes incoming in ripple fire, with one half a second behind the first, you can only ever target the first without using the 'Contacts' tab. It will show up when you 'target highest threat'. After it's destroyed, the next one will. But it's not possible for 'screening shell' turrets to lock onto them successively in that time frame.
Basically, if you've got many torpedoes coming in waves, you're only going to be able to use your screening shell against one of them. Since ED doesn't have a standard button for 'ripple fire' (which appears to be standard in modern fighters with banks of rockets/missiles), chances are they were unaware of this strategy, so they don't realize a means to defend against it is necessary.
Basically, the only way we can functionally target missiles that are locked onto us in combat is by 'targeting highest threat'. And that's fine. If there's one missile. It's entirely insufficient if there is more than one.
I know that sometimes my system will think a dumbfire rocket sitting bugged in space is the highest threat in a crowded CZ, and that's not very good.
As for my frag cannon screening shell turrets having to track and miss? When set to fire at will or set to target only, it knows when the target is within its optimum kill range. I'm assuming this would still be the case if it was given the same targeting priority as my point defence turrets.
Basically, it's like the combat system doesn't really know what to do with incoming missiles/torpedoes/mines, and it can be problematic when FDev balances their usefulness against a ship's shield generator.