I think that if this is your conclusion, you either didn't play Wrath or don't know why Arthas allowed what transpired on Northrend to occur (which was very blatantly stated in ICC).
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This is a lot of groundless speculation regarding the Scourge champions, especially given that if Arthas had succeeded, we would have been the Scourge's champions. Effectively Arthas winning would have meant that it would have been a single, unified front to face the Legion and the agents of the Void, and we decimated the Legion and the armies of the Void while busy being at each others throats.
If the Scourge had won, every major threat we've faced since (which is realistically just Deathwing and the Mogu/Mantid as WoD through to BfA would never have happened) would either be dead or under the banner of the Scourge.