OPAL solves a problem that OPA doesn’t solve at all (on purpose BTW - because the folks behind it want you to pay for Styra DAS, but you didn’t hear that from me 🤫)
OPAL solves the problem of running policy agents in scale in keeping them up to date with the various policy and data each needs.
While OPAL allows you to consume policy and data from various sources - it doesn’t replace those sources.