Razor leaf is like having hundreds of knives thrown at you simultaneously. Hydro pump you basically die almost instantly. There’s a reason water jet can be used to cut metals.
A firehose for comparison is usually minimum 200psi. Close up would hurt really badly but the chances of dying aren't great. At 20ft away you'll just get really wet. Their numbers aren't wrong but the analysis of what the numbers mean is probably pessimistic for the Charizard.
I do always feel rather safer drowning in water vs a mile in the air or at a volcano. But I'm afraid of heights and allergic to lava so I may be biased.