Category Best Seller Lagging in Search Rank

[Fotm]

I manage Amazon for a business with a unique product with one major competitor. We run a good business off one product (>$1M/mo) and have had strong success with PPC. Over the past year we've overtaken our competitor (estimates show we sold over 1.5x their volume last quarter) and we're consistently #1 BSR in the specific category we operate in, with them at #2.

On top of that, we have more reviews (7k+), better ratings (4.8), and have had our product listed for longer than their current product (they used to be the #1 seller but created a new listing a year ago for a new version of their product.) We're going on 4 years now.

After all this, we still have #2 organic rank for most of our top non brand keywords. Our product is pretty well optimized for these with the terms showing prominently in title, bullets, description, and A+ content without being overly stuffed or spammy.

At this point I'm stumped as to why they might outrank us. Maybe because their price is cheaper (though again, we have higher BSR thanks to brand preference) Maybe they're getting more traffic in from offsite? I'm not sure. Any ideas on how to optimize from here?