I said NO. The big bikes have not killed anything. The segment is more popular than ever because these big bikes have gotten more people out there, giving it a go, and they are doing it more comfortably, taking stuff with them you can't on smaller bikes.
"My opinion is that Austin Vince is a pompous ass"
I have to agree. You can adventure tour on anything of any size. He just couldn't afford one at the time of his original trip. Nothing wrong with his choice. There's just better options now.
Small bikes are great. They are agile and easy to pick up. But the lack of power sucks. Ever been to the desert on a 250-400? Sand saps power easily. Killing the engine won't get you anywhere because it bogged down due to lack of power. You need at least 600 cc on an adventure bike. Loaded up, you need more. The mighty CRF450R does fine in the dunes but it weighs 260# fueled and has 55 HP. A small, 400 lb adventure bike + luggage/tools and larger tank needs another 20-30 more HP.
I had a F650 loaner once. Took it for some off roading...lots of sand where I live, and it was crap. Handled for crap off road and when the sand got deep, forgetaboutit.
I've got good dirt bike skills and pilot a 1150 Adventure easily off road with hard cases and tent and spare fuel/tools. I get everywhere a true off road bike goes, just slower. And I get everywhere else I want to go in more comfort. So I can put in longer days for 2 full weeks.
For those who can't ride a big bike, smaller ones are available. Buy them instead of slagging off those who are capable.
I can go anywhere a real dirt bike can go, even long harsh, rooted climbs that some people say you can't do. Said by those that have never ridden a big bike. And if they have and can't, they just ned to work on their skills and strength. It isn't for everyone. Myself and many others on various other make of big bikes do it regularly. But then again, we also race enduros.