I don’t think that’s particularly true. ST has reliability issues that can affect officially supported smartapps as well as community-developed apps.
One benefit to using a supported smartapp is that when you email support, they’ll help you troubleshoot, whereas they may tell you there’s not much they can do to help you with a community-developed app.
Another is that local execution is only possible with smart lighting, but my understanding is that what’s currently supported with a v2 hub running locally is unimpressive and not what was envisioned when the new hub came out a year ago.
I haven’t tried to use CoRE yet. If you’re having an issue with it, there are active topics on this forum to help troubleshoot. I’ve heard it can have a steep learning curve, at least in terms of using its more advanced capabilities.
Either way, in the OP’s case there’s probably no reason to complicate things more than necessary. Routines can be configured to trigger at a specific time without the use of any other intermediary smartapps.