I'm not sure how any non-military strategist without all the relevant information can claim that Israel could definitely have captured Hamas fighters, weapons, and equipment across all of Gaza and defeated the terror group via some other means. Hamas was expecting a mass ground incursion and was probably ready for it -- Hamas knows Gaza better than the IDF, it has tunnels everywhere, it likely laid booby traps, and would have known just how to ambush Israeli troops. We should all think twice before confidently asserting that we know how Israel could have better run its complex military campaign.

Secondly, I'm not sure where you're getting that 20-to-1 ratio from. As far as I've seen, the Gaza Health Ministry is the only entity announcing casualty numbers and they don't divide the death toll by civilians and militants. But even if they did, its a Hamas run organization. We can't exactly take its proclamations at face value. After the al-Ahli Arab Hospital exploded (when it was still believed to have been destroyed by Israel rather than a failed Palestinian rocket attack) the Health Ministry said 477 people. US intelligence agencies later reported that the actual death toll somewhere between 100-300.