If I may ask more about this insight Dan or others :
"Today, I came away with the insight that the swing really does stretch the hip flexors, bind the abs, and work the glutes."
I have just started a new strength program - used to do powerlifting lifts, 5x5, with weighted dips, chins. Then I had 6months of kayaking, some core work, good mornings, and the weighted dips/chins to try and fix some asymmetric strength issues (as mentioned in another post) - last week I began a new program (amazing how my strength dropped off) with heavy deads, weighted chins, weighted dips, good mornings, and now kettlebells - swings, goblets, and single leg deads (and still kayaking 1hour day). I love the kettlebells, and they've knackered me which is fine. Wish I had been using them years ago! I only do a 5x5 with the deadlies, and 3 days, 200-250 reps all up for the swings (2okg kettlebell).
The thing I found is that my dodgy hipflexor (possibly pre-fatigued) and the insertion to the upper leg (adductor region) seems tight/fatigued - I'm hoping it gets loosed liked your insight suggests. (The swings definitely bind the abs too, and works the glutes.) Wondering if you had any further insights on the loosing of the hipflexor?