A centralized product will always be more scalable and cheaper them something on a blockchain.
In that case they don't even need a blockchain but just a replicating database just like how RAID1 works, but then globally. The term blockchain is extremely hyped up and in most cases doesn't even bring that many advantages to centralized incentives. If you want to become hot and potentially worth more as business, jump into blockchain. It's a trend that the general public likes a lot.
Not sure how much valuable input it has since it only concerns some basic tests, but Western Union CEO pointed out that XRP isn't bringing any significant advantages and doesn't provide the efficiency XRP initially advertised with. I honestly don't even think they need XRP at all. Nothing prevents them from creating a way better alternative that will be allowing them to do everything they want, but without using an external entity to do it.
Western Union is the third party already when people want to transact, and when XRP comes in place it will be the fourth party sticking its nose in something it doesn't have shit to do with.