I think
Faithless Looting is a lot better than Gamble for this strategy
It's basically "R: Draw 2 cards. You may cast 1-2 creatures from hand without paying their mana cost." That's extremely strong value.
Then it flashes back for 2R, which means you can either use it twice or you can pitch it to a discard outlet and still have the spell to use later.
Gamble is better in combo decks that abuse a specific degenerate combo piece, e.g.
Echo of Eons or
Underworld Breach, with highly assymetric power level, where getting one engine card strongly outweighs any risk of losing anything else in your hand. I tested Gamble heavily in many combo decks and ran odds on it. It performs best when it has <25% chance to do anything harmful to your hand (i.e. you don't care about discarding most of the cards as long as you get the card you wanted) and does something broken the rest of the time. It's much weaker in decks where there are certain cards you want to discard and others you want to keep in hand, since you have no control over the discard. It can backfire too often and just lose games. It's just bad in fair strategies, as card disadvantage and an unreliable tutor. This isn't quite a "fair" deck, and there are multiple cards we want to discard, but it's a bit of a hybrid between aggro and combo, and the power level is much flatter than engine-based decks like Echo or Breach.
Looting won't always find the exact card we want, but it digs into 2 new cards to increase the selection of cards we have access to. It can put 2 new useful cards in hand, something Gamble can never do, and performs better when the deck's average power level is flatter (i.e. there is no one broken card we want, and many draws are roughly equivalent in power). It doesn't excel at either digging for an answer or as a discard outlet, but it does a good job of playing a hybrid role for more grindy potential. It gives us the option to play slow through graveyard hate, and it can flashback to help us recover if the first wave is stopped.
There's a reason Faithless Looting is in almost every competitive Red GY-based deck in Modern and Legacy and was eventually banned from Modern. It's like the Brainstorm of these strategies, not degenerate or explosive but increasing card selection and consistency.
It could come down to player style. Some people prefer playing the lottery for the fastest explosive goldfish, accepting variance happens. Others prefer running card selection to reduce variance, at the cost of some explosiveness. Even with my combo decks, I usually end up running Xerox cantrips for card selection while others may try to run more explosive mana for turn 1 goldfishes. I run Brainstorm in any deck I can sneak it in. I like the dynamic decision trees offered by cantrips in real interactive games, but others enjoy the thrill of luck and explosiveness.