An excellent blog post comparing the two stacks:

https://blog.takipi.com/grafana-vs-kibana-how-to-get-the-most-out-of-your-data-visualization/

Grafana and Kibana have two well-defined, yet different, directions for visualizing data, and they reflect this in the sources you can pull data from.

Kibana focuses on helping you search, explore and analyze log data stored in Elasticsearch, and that’s the only source it supports, if you’re not using Elasticsearch then there’s no point using it. If you are, then its integration is tight and well developed.

Grafana offers inbuilt methods for connecting to over 30 data sources, including Elasticsearch, and focuses on visualizing time-series metric data, which can be logging data, but is better suited to visualizing data from constant streaming sources, such as sensors and metric reporting.

https://db-engines.com/en/system/Graphite%3BInfluxDB%3BOpenTSDB