The routing automatically routes you to other inference providers (for the same model) if/when the original provider goes down.

It's a convenience cost, for sure, but it's not valueless in a fast-moving world. Certainly if you're comfortable with one provider and it's cheaper, do that.

For me the largest value-add is the unified API. Being able to instantly start trialling a new model with zero code changes is well worth 5%. The other part is not having to deal with billing for multiple platforms.