You are confusing the meaning of the 'lead' in canter for the one that's often used to describe the leg that a horse lifts first when going into a trot.
If you're riding on a circle and you automatically rise on the first stride that the horse makes in trot - the 'leading' stride then its important if you want to be on the right diagonal that you recognize which leg you're posting on
No, I am not. The trot does not have leads. The human can have diagonals
Show me one English equitation pattern where the word 'lead' is used in any trotting. It is incorrect terminology There is no leading leg, although there is a diagonal pair and you can set a horse up for a correct lead departure at a canter, but for a trot, the rider will first sit, then pick up the correct diagonal, depending on direction
Most people do not have the strength nor does the horse have the training, to start from a two point position, as this pattern calls for GoHorseShow.com | Breaking Down the Congress Patterns: Hunt Seat Equitation - GoHorseShow.com
At any rate, if you wish to say find your diagonal according to lead stride legs,( inside front, outside hind) that is one thing, but to say a horse has leads at a trot is incorrect Any show I have ever been at, or any clinic I have ever taken, confines the word 'leads to the canter and diagonals for the trot
Never heard anyone that knows their equitation , ever tell someone that they are on the wrong lead at a trot. They are told that they are on the wrong diagonal.
Never in a rail class, have even been knocked down if it takes two strides to get that right diagonal, versus a wrong lead departure at the canter