Israel has killed dozens of Hamas leaders, but way more fighters. There's no way to know exactly how many, since Hamas doesn't even pretend to put out numbers that separate civilians from combatants.
The 8k number also comes from Hamas, the same people who said that 500 people died in the hospital explosion (and blamed it on Israel). Go see the estimates literally anybody else made. All of these numbers come from Hamas.
That 8k number also includes all deaths, not just at the hands of Israel, but at the hands of PIJ and Hamas themselves. Hundreds of their rockets have landed in Gaza, and they've been known to execute their own. They really love to blame Israel for these deaths, though—not just in the case of the hospital when they can make up a specific cause, but in the cases you've never heard of where, oh, there's rubble, what caused it, don't worry.
The death of each Palestinian civilian is a tragedy. Hamas provoked the war, Hamas is killing as many of them as anybody. Israel is engaged in remarkably precise targeting of enemy combatants and places an entirely unprecedented effort into warning them when they're about to strike.
This is urban warfare. This is what Hamas called for.