For most queries, that might be true. However, the termination guarantees of Description Logic (OWL) reasoning and SPARQL (more precisely: the specific time complexity bounds) immediately imply that Prolog is more expressive. Even if we don't consider such ridiculously long-running queries, there's still limits to what can be expressed in DLs and SPARQL: since OWL doesn't have any variables, you're restricted to tree-shaped queries (indeed, this is a major part of why OWL reasoning is decidable), and SPARQL doesn't allow you to express any constraints on the intermediate nodes in a property path expression. Neither of these restrictions exist in Prolog.