I think using the RCS can raise legal issues if Google/Apple collects the messages, especially if you're in the EU. I don't remember how RCS works and I heard it can be E2E encrypted but seeing the comments makes me less sure about the safety of using it in a business environment. SMS isn't encrypted at all and easy to intercept but there's less chance of it being automatically collected for marketing purposes.
Using apps is better tbh unless you make your own apps to create more bloat and fragmentation. Here where I live nobody uses SMS anymore.