It's not conclusive you know. If 17% CAGR is true, there may be three explanations which are not mutually exclusive. The first is the use of leverage on the holding level, the second being unlisted subsidiary companies accounting for the largest gains, and finally the transfer/sale of state assets to Temasek at book value (at cost) instead of some estimation of its possible market value. Personally I believe the third accounts for most of the supernormal returns enjoyed by Temasek. To say that the state achieved 17% CAGR under the stewardship of Temasek seems disingenous but that is just semantics to fool the masses. No biggie.
Using excessive leverage for private investments on the other hand... things can turn sour pretty fast.