From my limited research looking for authorization systems [1] it is but it is not: OPA can get actually quite slow for "real world" production scenarios. For example until recently Ory Keto used OPA and had that issue https://github.com/open-policy-agent/opa/issues/1443 . It seems to me that Oso although is based in Opa and Zanzibar ideas, it may have some performance improvements and ease of use.

[1] (we are planning to change a half-assed internal auth system to a pre-existing one)