OwnCloud needs webDAV

Look forward to getting hacked - maybe a lesson will be learnt, the hard way.
Just because you think you have a solution doesn't mean it is right.

Nextcloud/Owncloud uses sabreDAV, not Apache DAV.

RTFM

You don’t need the WebDAV module for your Web server (i.e. Apache’s mod_webdav), as Nextcloud has a built-in WebDAV server of its own, SabreDAV. If mod_webdav is enabled you must disable it for Nextcloud. (See Apache Web server configuration for an example configuration.)

Mod Security
Disable any triggered rules - do not disable modsec.