I think there are a few oversights worth mentioning:
Serrated Dirk is a very overpowered item and early game power spikes matter. So the difference between Kraken + Dirk and Kraken + 2 Long Swords is a pretty big deal. Or even just Serrated Dirk vs. the components of a Noonquiver, since a LDR player will not combine much of anything in the early game.
The execute is relevant. Agreed that against squishies LDR does similar single-target damage and we'd expect to deal more against more durable targets. However, a 5% execute is more akin to a 5% damage amp to every champion on your team, because the last 100 health on the 2k hp Volibear is going to disappear regardless of who removed that first 1900. Considering these calculations are +/- 8 damage in the squishy case, I'll take +100 against melee champions every time. Even using enemy marksmen as the primary case, 5% of 1600 hp is 80. If your ability loop is dealing ~850 +/- 10, then it looks like the ...