I'm currently doing a series on the epistemology of atheism, the burden of proof, and so on. The next article, which should come out soon, is on agnosticism and its relation to atheism.

In general, though, atheists are much more careful about staying true to the available evidence than are theists. You seem to be assuming that the burden of proof is equal, and that knowledge requires certainty. Some knowledge, though, is probabilistic, so you can be uncertain without being agnostic.

https://medium.com/interfaith-now/do-atheists-and-theists-have-the-same-burden-of-proof-24a4bc0013d1?sk=ade555e68cef719b6d01fec2dba9371c