I can imagine it's even a bit worse, in that it's likely the DNC recruited Buttigieg in order to consolidate and motivate younger moderate-leaning voters as well as LGBTQ supporters, while Klobuchar was recruited to do likewise with middle-aged moderate-leaning women. I think it's highly unlikely Biden could have garnered much support from these groups on his own, and much more likely that those groups would transfer their support of Buttigieg and Klobuchar to Biden.

. . . sheer speculation.
The Democratic primary voters (lots of whom had very recently been undecided) made their choices. As David Brooks said on the Newshour tonight, they "acted as a community".