Every conflict since at least 2006, the Hamas health ministry releases casualty numbers.
Then after the conflict subsides, the UN sends in professionals to verify the numbers.
The UN has verified the Hamas health ministry's numbers as accurate every time.
I think it's important to distinguish between good faith criticism, like you are doing, and the people screeching that "I dont believe the 10k number bc its Hamas". The latter is genocide denial, it rhymes with "I dont believe 6m died in the Holocaust."
And yes I agree the fog of war is thick, the initial reports of 500 dead at al-Ahli hospital were overblown and sensationalized.
But I think the safe assumption is that the 10k number is a significant undercount. The health ministry counts corpses in hospitals and morgues. It isn't able to count people buried under rubble, bodies incinerated, corpses strewn across the road outside Gaza City, direct hits that leave nothing behind but pink mist, etc.
Look at it from the other side: Israel has said it launched over 9000 rockets, so if the 10k deathtoll is accurate, then each rocket killed only 1.1 persons on average. This death rate per rocket is very low, especially considering many are launched into heavily populated urban areas.