The exact sources and numbers one wants to use don't really matter. You're right that there's a high uncertainty, but only in details. The overall picture is quite clear and consistent. In Gaza, Israel is primarily killing civilians under the pretext of seeking out a relatively small number of Hamas militants. And they have killed a significant percent of the entire population of Gaza, which only had a total population of ~2 million.

For instance the Lancet carried out a study using a variety of sources for cross-referencing, including things like obituaries, and found ~70k deaths in the first 8 months of the war, a war that's now been going on for years. And those deaths they measured were also only those caused directly and immediately by Israel due to traumatic injury. Famine, disease, despair, an other such deaths are not counted and bring it up substantially higher.

Politics in the US waxes and wanes, increasingly between extremes. Israel has already alienated itself from one 'side' in America, and is gradually doing the same with the other. Consequently, the fate of Israel in the future is more uncertain than ever - imagine an Israel not only lacking US support, but with an antagonistic US government in charge. And they also aren't exactly making friends with Russia or China. Making enemies of the world as a micronation is generally not a wise path to go down.

As for Ukraine, there's similarly a clear picture. There's no doubt that civilians are being killed but there's also no doubt that the vastly overwhelming majority of all deaths are military. So the situations simply aren't comparable.