could our heroes have misjudged pitch, therefore speed and performance?
Well in maneuvering flight, yes, mountain flying can have many dramatically misleading visual cues. However, on takeoff on a level runway, it's pretty simple to establish your pitch attitude relative to the ground. Its pretty hard to over pitch a taildragger on takeoff, as the initial takeoff action is to lift the tail, thereby reducing pitch. If you cannot get the tail up - something is wrong.
If you don't lift the tail, it's akin to a three point takeoff, which equals a soft field technique in a tricycle, you'll still get airborne, if the plane is able.
Certainly examination of many characteristics broadens thinking, which is great. I've never heard of dry microbursts, so I'll stay clear of comment on those, though I have certainly experienced some [wet] ones from local cloud, and they are scary!
Thermals go up, so entering one of those can only help a climb.
Engine controls can certainly be set non optimally for certain conditions, and perhaps by not leaning the mixture there's a contribution there. It is unfortunate that pilot training has "everything full forward" for full power. Fine at sea level, but deceiving at altitude. I would hope that a pilot used to a high altitude airport would take the appropriate action - it's the sea level pilots who make that mistake once.
As for dust devils, well those I have seen are small, contain a lot of dust, and move horizontally. Not great to fly through, but easily seen and avoided, and really don't affect climb rate for more than a second or so.
I think the poor decision making is the prime factor here...