This!
The exercise I mention above creates the muscle / feel/ ability to keep the canter from being underpowered while not butt in tack.
On hotter, naturally forward horses (5 years) I never realized I lacked this ability because the 4 consecutive horses I was leasing didn’t require me to create the energy - they required me to contain and direct it so I never realized I COULDN’T keep a quality canter without sitting! And as a former dressage rider for most of my junior years 12-18… I forgot that half seat on the flat existed.
The canter, as always, is what makes the course. less than 1/10 of the strides are jumps - the other 90% is canter. Or at least that is what I tell my former (inner) Dressage Queen self.