Of course, the card is also great in Commander
Since then several Extended decks have fit the bill, and they were all far more abusive and dangerous
I do not have Pact of Negation in my cube presently however its value rapidly increases as the number of suitable archetypes for it increases and with cube design being as diverse as it is you can easily include more of those archetypes from one of a few different approaches
As for Cloud himself, he can immediately attack on entering the battlefield, and attach an Equipment straight away
I liken this set to Legends in a way, because they both contain so many unique legendary creatures with a surprising amount of value
Obviously that all gets thrown out if you play a desert-centric commander like Yuma, Proud Protector or Hazezon, Shaper of Sand, but its better to analyze these cards on their own and not in the context of an individual card that makes them much, much better