I think that's true, but mainly because Israel are picking up the pieces in relative peace whereas Gaza is under siege, pulverised and half its population displaced. Information gathering's likely somewhat disrupted.
I'd also agree that Hamas has incentive to inflate figures. Should be said, though, that last time thousands died in war (2014), Hamas, UN and Israeli figures for the Gazan dead were pretty close (2,310; 2,251; 2,125 respectively). They did differ in the proportion of civilian/combatant though. Basically a lot more fighting age men were killed than should be the case in indiscriminate attacks.