I think you misunderstood his arguments. He's stating that favouring a Result-type monad (as opposed to using exceptions that may never occurs) leads to boxing

I think you misunderstood his arguments. He's stating that favouring a Result-type monad (as opposed to using exceptions that may never occurs) leads to boxing of values inside a tag of a union-type. Threading exceptions handling where exceptions are never thrown in practice typically little cost. However this is really different from boxing of value-types in a situation where you don't have access to generic collections for instance and as such we're talking about a different cost. Unless you're entire application is passing integers or floats around (and not proper objects/records) it's highly unlikely the pattern is causing the situation he described.