The short answer to this is no. While a wider deck does ensure greater coverage, it might also compromise maneuverability. Mowing your lawn is not all about actually mowing since there’s a lot of turning to do as well. If the time spent adjusting your direction and overcoming obstacles exceeds that saved due to the increased deck size, the efficiency reduces.
Power and cutting quality is another thing to consider. A wide-deck mower that leaves the lawn crying for another pass is highly unlikely to become a time-saving device as compared to a smaller one that actually delivers.