Statistics will be nothing if old age catches up on Donaire. This is one major reason why legendary boxers even though have better statistics losses to the young ones. And one of the reasons why Manny Pacquiao won against Oscar Dela Hoya.
But Alejandro Santiago can't be considered to have the same performance level that can be considered currently in super prime.
Nonito Donaire also remains active fighting in the year and that shouldn't give him a rusty performance.
Santiago also doesn't have impressive wins against boxers at the same level as his prime. Donaire just experienced the toughest challenge in his career when he faced Inoue at 40 years old. At the same age, Donaire can surely handle Santiago without a doubt.
Making up some comparison in between their past fight performance, prime to prime then we could really be able to determine on which one is better but Donaire is getting old now
but i do agree on those words that he wouldnt really be giving out that rusty performance.