I wouldn't call them the same as Databricks SQL runtime is a bit different (not everything is supported for example UDFs), new releases are separated from standard runtimes updates: https://docs.databricks.com/sql/release-notes/index.html

Databricks cluster can handle notebooks. SQL endpoint is only for SQL queries.

Both can be in photon or non-photon versions. Photon has a bunch of improvements for example better handle small files problem.