We already know that both Moro, Cell and Majin Buu have showcased very similar abilities in the past. All three fighters are different but have all shown to increase their powers with a kind of absorption and they’re not the only ones to do so in the Dragon Ball world.
However, the most recent Dragon Ball Super manga chapter just made that power as useless as what fusion now is and in the same arc, fusion was made redundant as well. How? Well, Goku kindly sat down and explained to Moro that everyone has a limit and absorption doesn’t allow one to surpass the limitations of one’s body.
Only training and teaching your body to access an increased level of power will enable a fighter to use that power. Yes, characters like Buu and Moro have used absorption to increase their powers in the past but as the Dragon Ball Super manga just confirmed, this method has its limitations.
If either Buu or Moro was to absorb power that exceeds their body limitations, their body will break down and be consumed by the power and kill them. This is what’s happening to Moro now, as he has consumed too much power for his body to maintain.
A way around this is for either Moro and Buu, or anyone who uses absorption, to train. This will allow their bodies to grow, which will enable them to retain and utilise more power. So, all our theories about Buu absorbing Beerus and Jiren if needed as last resort are not redundant as well.
Therefore, as you can see, absorption on its own has been made redundant by the Dragon Ball Super manga. It doesn’t mean that it’s useless but it means that it’s no longer as overpowered as what we once thought it to be in the past.