There are plenty of board wipes that cost six mana, making Catastrophe's cost not too high to pay
The recurring value-oriented nature of Sun Titan targets lend themselves naturally to Restoration Angel-based strategies, such as Yuuya Watanabes U/W Control deck from Worlds 2015: Creatures (16) Lands (26) Spells (18) While Dragonlord Ojutai is sturdier, Sun Titan can be invaluable for going over the top of opponents, for actually ensuring hes got enough advantage to close it out
There are many ways to make a creature big in Modern, and there the 3 Energy can yield many more +1/+1 counters
I personally love how it creates team play: usually in Magic , you play against somebody, but in Archenemy, you get to team up with people
SP decks especially love it since finding Pokmon SP early allows them to quickly put 3 in play, so that they can threaten to use Power Spray