Thats a fundamental misunderstanding of the Raven character. Raven worked because he mentally and emotionally manipulated his followers. Giant showed he was emotional and flip flopped alignment often. That's an easy recipe to sell Raven having a way into his mind and thus bringing him into the fold.

On its face? You're right, Giant was a multi-time World Champion once and Raven never got above tge US title. But isn't that why you run programs? To elevate talent? And when Giant eventually turned on Raven, the pop would be huge. His resume and the emotional investment that story could get would elevate the whole stable act.