So if it's a matter of concealment, IMHO the point is moot.
You have a reasonable point about the length of a cover garment and concealment.
I'll argue there are two key points in concealment, 1. covering the length of the muzzle, which is your argument, and 2. pulling the grip close to the body.
1. With an IWB holster, your cover garment doesn't need to be as long as the cover garment would need to be for an OWB holster. Admittedly, with little guns like some are discussing, like the S&W Shield or the SIG P365, with most concealment OWB holsters, there isn't much barrel length extending below the bottom of the belt, so the cover garment length requirement isn't much different between IWB and OWB, but it still is a difference. With a big gun, like the FN you pictured, or a G34 or 1911, it could be the difference between wearing a t-shirt as a cover garment or having to pick something longer than a sport coat.
2. The second concealment issue is pulling the gip close to the body. Little guns are also less of a concern in this area since their grips are so short, but the key feature of any OWB concealment holster is the trailing loop that pulls the grip of the pistol close to the body.
Using the Milt Sparks catalog to make the point would be examples of the 55BN (
https://www.miltsparks.com/products-55-bn.php ) a Nelson #1 Professional with a tunnel loop and trailing loop, and the i-Bak (
https://www.miltsparks.com/products-i-bak.php ) a modified Baker Pancake that has a loop in front of the pistol and the trailing loop. Both designs pull the grip of the pistol close to the body to aid concealment.
Without the trailing loop, on a holster as your recommended Dara holster, which would be considered a competition/training holster (the Sparks equivalent would be the 1AT - you'll have to search the Gallery -
https://www.miltsparks.com/gallery.php#swipebox ), and with the retention device a duty holster, there is nothing to pull the grip of the pistol close to the body.
Most IWB holsters don't need the trailing loop feature since the holster being inside the pants provides this function anyway, but many holster makers add features to their IWB holsters to increase this effect.