Using Delta Chat, which was your question. Delta Chat only requires an email server, so if you already have one because you build and make them as part of your work, it is a no brainer to use DC and benefit from self-hosted E2EE and easy comms. You get full privacy and control and E2EE - that's a huge benefit over the other platforms you mentioned. The only drawbacks are:
1) You don't self-host so now you don't get the privacy and/or control
2) Delta Chat lacks mature group / moderation controls
3) Delta Chat lacks proper integrated video chat, but/and it does do Jitsi
4) Delta Chat is slightly weaker on meta data leaks than some other offerings (e.g., Simplex)
But, as per your question ... if you already have a self-hosted email server and domain ready to do, DC is a no brainer for an immediate switch and likely a net positive for privacy, control, and E2EE.