The idea and concept of the Lump sum buying entails buying right away, it has alot to do with investors decision to invest right away with the available huge amount without considering market condition, maybe you are describing buying the dip instead of a lump sum buying,
I mean, if the market condition is favorable, then yes, 'Huge sum can be invested', this is lum sum investment all by itself.
Investing at a favorable market price is a plus point 'if achievable,' otherwise, it depends on person to person 'depending on the market condition they want to invest in.'