You forget about one smaaaal issue: disposal of created antimatter. Also why bother creating matter from energy when even today we are able to create stockpiles

You forget about one smaaaal issue: disposal of created antimatter. Also why bother creating matter from energy when even today we are able to create stockpiles of raw elements (although quite inefficiently and with almost no control over isotopic composition). Assuming that waste will be converted back to those elements, you don't need those stockpiles be too big and energy consumption will be modest when compared to creation of matter directly from energy.