The wiki is unclear on Pluto's legos.
As for Lakshmi's bonus damage at corrosion 4 thing, it's implied to be a separate attack entirely type deal, as it has its own soft cap of 450k.
Now, my inference there is based on awakened Acala's burst effect being additional damage against raging enemies. AW Acala's burst effect is listed as 80% of normal burst damage and has its own soft damage cap of 500k. It is also explicitly noted here that this is a pursuit type thing which is not included in burst streak damage calculation, in contrast to Uriel.