Uriel repeatedly points out that Harry sees things "from a different perspective" and have even called it "limited". Perhaps that reasoning applies to the readers too. As was pointed out above, the gift of soulfire has the direct, immediate effect of saving Harry's life. It seems likely that Uriel has a form of omniscience similar to what we've seen out of the Mothers, able to see many possible futures, contingent on the decisions of free-willed mortals. Saving Harry pays tons of dividends down the road, which is the true "weight" to use to measure the "balance".
With Harry's life along with the gift of soulfire, and all he will go on to do with both, the scales do appear close to balanced, even if you include both circles on the other side. You just need to see things more from the perspective of an angel.