If “other poster” means me, my main point was that, looking at flights that are survivable by at least some adults wearing a standard airline seat seatbelt, a car seat (FAA approved) will greatly increase an infant or child’s chance of survival over lap-infant, child in seat without car seat (only standard seatbelt), or any other form of transport - up to the age at which car seats are no longer recommended.

There is a reason car seats are mandated in (every?) most states for children up to a certain age - yes there are unsurvivable car crashes (T-boning a semi truck, for example) but putting a child/infant in a car seat greatly increases the chance they survive a generally survivable crash.