Some aeroplanes can't dump fuel anyway, so if there's a fire you just land overweight.
For those that tried to delay their landing whilst dumping fuel, or diverting somewhere other than the very nearest place, it didn't end well, there's a moral to that story.
If you are on fire, LAND NOW!! If I could dump fuel then maybe I would, but I wouldn't be overly worried where it ended up as long as I ended up safe and sound.