Would you want to evacuate from a 747? Cripes, no thanks. Even leaping from the main deck would be akin to a two-story rubber slide, let alone the top deck which would be a pretty scary proposition. Broken bones aplenty.
One shouldn't be cavalier when considering evacuation and it's always a tough call - I'm thinking the 737 in Okinawa went up quickly - but I also know that ponds of Jet-A1 aren't as risky as people think.
I had a serious leak from a 737 last year, with a veritable lake of the stuff. The fire service (major UK airport) were very relaxed about it and in fact asked us not to disembark because they feared an orderly disembarkation in itself might panic people unnecessarily. I have to admit feeling somewhat uneasy...