A lot of that stuff is skill level and bike prep (gearing, porting etc..)
Most of my starts just about everywhere and just about on anything is 2nd gear even on my 1974 YZ125A.
The 125 is wound so tight you almost have to start in 2nd gear (5 speed).
My 500 is so powerful, again, you almost have to start in 2nd gear (92 close ratio).
A slippery, loose start can qualify for 3rd because you'll be looking for it as soon as you start rolling. Better to wind it up and slip the clutch a little for smooth traction and skip a shift.
My 480 is a 4 speed and I still start in 2nd gear.
I consistently get great starts, motocross and cross country.
I'm just a wuss when it comes to the first turn pileups.
I'll be on the extreme inside or extreme outside, if I don't get a clear holeshot I just cruise the first turn and THEN race.
I love squaring turns and stuffing my friends!
Of course, there's always the roost factor after you stuff them
btw-Is that you and your dog in your avatar? It's cool.
Sorta looks like my dog Arthur.