This is a known issue with non-creator events, unfortunately. We have some improvements coming in 2.6, but as you'll see on the ticket linked below, there remains work to do:
Part of the issue is also how the ISAD standard (and consequently, the recommendations the ICA strongly advocated for when we were first designing ICA-AtoM) only supports creation and accumulation events. Other templates that support more event types will display them in the body of the record more prominently in the Dates areas - with ISAD, even after the fixes they will be displayed in the sidebar, and in the name access point area (ideally with qualifiers).
I was hoping we could finish addressing the outstanding feedback on #12718 for the 2.6 release, but at this point we are moving to testing and packaging, so further work on this may not make the cut. I'm hoping we can return to it in a future release - though the additional enhancements outlined in Wishlist ticket #12719 will likely require sponsorship for us to implement.
Regarding the warnings about creators - if you're using ISAD and a custom event that ultimately will end up meaning the same thing as creator (for example, there are cases where "author" of a book would be the same as creator - though not always), then you may want to stick to creator where possible. Either way - just know that those warnings will never be shown to public users. With the fix coming in 2.6, these names will be available in the Names search/browse page facets, and they will be indexed - but again, not as creators still.