That claim is a big lie from start to finish.
The Lancet DOES NOT believe that in the slightest. As I'd assumed, you've been lying all along about the Lancet.
The Lancet, itself, conducted no such study. The Lancet is also not making any claim at all as to how many are presumed dead. They are simply reporting that a study was done (by a Lebanese radio host and a cardiologist neither of which qualifies them as experts). It is the same as reporting that a political poll was taken and these are the results of the poll.
The Lancet is not in the least vouching for the findings of this study. Just reporting that this study was conducted.
As well, the study does not say that Israel killed those people. The study is simply estimating (using lots of significant assumptions and accepting Hamas' numbers at face value, which is a joke) how many have been killed but are attributing no blame or how the deaths occurred.