I think Gero was expecting himself to be actually stronger than SSJ Vegeta. He already knew Vegeta knew about the absorptions and I think he would expect Vegeta to be cautious about that, not like Goku, whi fired off a Kamehameha (though Vegeta was a bit reckless shotting that blast).
It's implied that all the humans and Piccolo (heavily suppressed) are still below base Vegeta, and you could not work with Gero statement unless you change the SSJ multiplier, otherwise Gero would be expecting to beat Vegeta by absorbing powers that are at less than 2% of his SSJ power.