@DragonicDoom Disregarding the NLF, the problem though is that Osmosians's power absorption does have limitations, one being in terms of the amount of energy they can absorb at the very least. At least from what im getting on
their page on the Ben 10 wikia .
An Osmosian needs to train in order to use the energy they absorb effectively, as well as maintaining the rate of absorption. And even then, the process is risky and can have side effects if it is not carefully done. This already suggests that an Osmosian cannot absorb any level of energy they choose and make use of it immediately. Compare this to absorbing a Celestialspaiens energy.
Even Celestialsapiens
themselves need tens of thousands of years after being born in order to even be considered developed before they can use their powers. So Aggregor being able to make use of them before they themselves can sounds very absurd to me, which wouldn't benefit Aggregor at all unless he was just absorbing their hax abilities.