This is only true if the vast majority of donations are small. Bernie Sanders was "knocking it out of the park" in 2016 with millions of people donating small individual amounts (me included). For example, $137 million from 4.7 million contributions.

I have looked but can't quickly find comparable numbers for Biden. That I can't find the info after searching for 10 minutes says a lot (I'm good at finding such info on the interwebs). What we don't know is the median donation.

I saw an average donation from 2023 for Biden of $39.

My guess is that Biden has raised a shitton from some really big donors in large donations (e.g. $25,000 a plate dinners).