Delaying elbow extension to help prevent finishing the reach back too early as a contributing factor to increasing the risk of the shoulder angle from collapsing seems to be an under appreciated topic.

Here's some other helpful information to prevent the shoulder collapse:

Hunching the shoulder forward and keeping it hunched during the throw instead of pulling the scapula back to pull the disc. You'll see pro's have their shoulder still hunched forward as the disc is ejecting.

The pull through then happens from the offarm pulley effect (requires hunching) + the elbow drive as Holyn Handley shows here:

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Watching the Kyle Klein clip in this video and others who do a similar move, bringing the disc into the body first before reaching away wide made me think of adding an "in" to the front of the famous "outinout" phrase. Trying this timing move out has helped with my reach away timing to not be too early:

IN when xstep lands bring disc into body with elbow bent as you begin to coil
OUT then reach away from your body wide (not back)
IN to power pocket. Bringing offarm in with throwing shoulder hunched forward will start pulling you into the power pocket bringing the disc back in close to the body, then also drive the elbow forward across the chest
OUT elbow extends out of the power pocket to accelerate and eject disc