AUM is debt .. so its value depends on what is being done with it. To what extent that these assets can be used for "financial engineering"? They seem rather illiquid to me (and apparently the market, which feels that BlackRock's 11k employees and $4.2 trillion generate less than a third as much wealth as Facebook's 6k employees and $18 billion in total assets "under management").
And how is funding successful new companies not wealth generation? Y-Combinator has invested a total of ~$10m invested for approx a 5% share of ~500 new companies with a valuation greater than $20b and growing. It's annualized RoR is north of 50% for nearly a decade, and likely to increase henceforth.
By contrast, Berkshire Hathaway grew at ~20% for ~50 years. I predict YC will blow those numbers out of the water.