Then if you're trying to make a camp fire with the sort of rain saturated wood you find in the Pacific NW or the UK at the wrong time of year, you will probably fail and certainly struggle. To say that no one needs a +6 inch knife is even sillier than those people who use BK2s to do jobs a Mora is better for. If you need to split thick wood for dry tinder, a large knife is useful. They're also great for making feather sticks used draw knife style.
You can survive fine in the conditions that you are used to. But you're not some universal survival expert who has experienced absolutely everything: another example of the need for a large knife is the use of a leukku for slicing pine branches in the cold - one chop will do them, but with a puukko they're an absolute devil. Are you really going to claim to know more about how to survive in a Scandanavian winter than the Sammi? And Finns and Swedes favour Hukaris - cleaverlike things that chop and split like a large Busse (but cost a lot less) - too.
That said, for what I do "surviving" in the outdoors I've never needed more than a SAK. I just don't mistake my needs for those of the entire world.