[wqaatwt]

> replaced the previous European population

Primarily the male population. Genetically much higher proportion of the female population survived.

Of course that’s an exaggeration as well. In much of Southern Europe and other areas the replacement was far from full.

[acadapter]

Maybe this is how the branches of Indo-European evolved.

Laryngeals replaced by vowel lengthenings, merging of consonsants, vowel shifting based on other sounds, etc. It's like there were many different events where "Indo-European with a heavy foreign accent" suddenly emerged.