1) Could inconsistent spines cause the problem I've outlined?
Absolutely. Carbons are extremely susceptible to this issue, some from the get go, some over time. It's why I had no problem laying down the cabbage for ACCs.
2) Wouldn't heavier arrows tend to smooth out this problem?
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Perhaps a tad, but personally I would rather remedy the issue than try a band-aid.
3) What are the ramifications of shooting heavy arrows? I'm looking at 500+ grains on a 55 pound draw.
More KE and momentum, greatly reduced trajectory.
4) Could it be that the situation I've described is more common than most people know?
IMO matched weighted and properly spined arrows will show one their true shooting ability. For years I assumed I wasn't as good a shot, ACCs fixed this problem overnight. Thank you JeffB...