I thought it would make sense for dedicated armed responders to have a shoulder-braced firearm readily available. Concealed handguns make the most sense for people that aren't part of the security team (or whatever term is used for people designated by the church to be prepared for an armed response), and the security team should certainly have them, but for those that are in cooperation with the church to provide security, it seems to make sense to have some carbines or PDW's available in quick-access hard cases -- for example, one in the sound booth, and at other strategic locations where they are accompanied by a team member (perhaps to the sides of the platform, and from where the doors can be watched). A security person near the threat would probably respond with a handgun because it is quicker to access. But if someone were to be clear across a large auditorium, the extra time to retrieve a carbine with an EO Tech and suppressor from a quick box before they engage the distant threat seems well worth it. We could debate the overpenetration issue, but it's really no different than it would be for law enforcement that similarly works in crowded environments and besides, some PDW's are just pistol-cartridges with barrels no longer than a handgun, but they have that shoulder brace and rail for a large optic, and can easily accommodate a suppressor without making them awkward.
This isn't my advice or recommendation to the OP. With only one person, it doesn't add much value since with only one, it will probably be in the wrong place and need to be secured (and less accessible) when unattended. Maybe a person could have the smallest PDW in a backpack, messenger bag or satchel, but they'd have to remember to keep it with them. It's probably more trouble than it's worth.