The game is really designed and balanced towards heroic roleplay - and not towards a realistic simulation. When heroes are in the heroic tier they've got dozens of hitpoints.
When you look at the game on the scale of things that are a mere fraction of the power of those heroes, the math begins to break down. There's simply not enough room in the very low power strata and not much of the designers valuable time to be concerned about fine-tuning balance of threats that will no longer be credible by time our characters are 3rd level.
I do recall a similar discussion in the days of 3.5e: Commoner vs Cat that translates well from 3.5 to 5e - it's worth looking at the mathematical analysis.
Also, I should add that this is an extension of the classic commoner vs cat conundrum that dates all the way back to the earliest days of D&D.