Minor nit, but GitHub's gh-ost tool is for performing schema changes, not data migrations. You may be thinking of Shopify's Ghostferry? Anyway though, your bro

Minor nit, but GitHub's gh-ost tool is for performing schema changes, not data migrations. You may be thinking of Shopify's Ghostferry? Anyway though, your broader point is absolutely correct, re: data migrations typically involve complex custom/company-specific tooling at scale. And it's also difficult to map data migrations to a declarative tool in a way that feels intuitive.