That Disco was built in a bad position where it couldn't even reach the enemy base. Additionally it was completely mismicroed (if microed at all).

DRP is generally an area denial/bombardment weapon similar to the nuke. You don't need to/can't aim accurately so it's much better for cleansing entire areas than the other superweapons. It is also the only superweapon capable of penetrating very-very-late-game sandcastles shields due to its emp shell. Its position isn't visible without scouting, making it harder to counter than other superweapons. By having both a terraform shell and a very high firing angle it is nearly impossible to block by mountains/terraform. All of these advantages more than justify the extra price and reduced range over Zenith.

There are multiple reasons that the Zenith was more effective than your DRP in this match: The Zenith was built within range of the enemy base. The enemy moho could be used to amplify the effect of its meteors. The combination with a nuke allowed it to kill entire areas simply by sniping the protector.