Improved LootEntry#getEffectiveWeight - Makes Luck apply a modifier to weight so all loot pools get impact from luck, not just quality. Code licensed MIT - Mojang can use as WTFPL/no restrictions - please pull this into Minecraft Mojang!

LootEntry.java

        // Refactor how Loot bonus applies - 
        // V PCT = Vanilla Percent Chance, M PCT = Modified Percent Chance
        /* base in these tables does not include vanilla quality modifer in this table, but does in code
                BASE    IMPACTED    REDUCED V PCT   M PCT   PCT CHANGE
        ITEM 1  400     12          388     26.67   27.75   1.087
        ITEM 2  100     0           100     6.67    7.15    0.486
        ITEM 3  1000    90          910     66.67   65.09   -1.574
        TOTAL   1500                1398

        LUCK (*10)  100

                BASE    IMPACTED    REDUCED V PCT   M PCT   PCT CHANGE
        ITEM 1  4000    1560        3220    31.74   39.03   7.284
        ITEM 2  100     0           100     0.79    1.21    0.418
        ITEM 3  8500    7140        4930    67.46   59.76   -7.703
        TOTAL   12600               8250

        LUCK (*10)  50
        */
    public int getEffectiveWeight(float luck)
    {
        // This is vanilla
        float qualityModifer = (float) this.getQuality() * luck;
        // Random boost to avoid losing precision in the final int cast on return
        final int weightBoost = 100;
        // This is vanilla * our weight boost
        double baseWeight = (this.getWeight() + qualityModifer) * weightBoost;
        // If we have vanilla 1, bump that down to 0 so nothing is is impacted
        // vanilla 3 = 300, 200 basis = impact 2%
        // =($B2*(($B2-100)/100/100))
        double impacted = baseWeight * ((baseWeight - weightBoost) / weightBoost / 100);
        // =($B$7/100)
        float luckModifier = Math.min(100, luck * 10) / 100;
        // =B2 - (C2 *($B$7/100))
        double reduced = Math.ceil(baseWeight - (impacted * luckModifier));
        return (int) Math.max(0, reduced);
    }

because mob loot pools have very little variance in weight, it does not impact them much unless mojang adds a higher weight item to pool:

300 witches no luck
69 redstone, 78 sugar, 88 gunpowder, 69 eyes, 69 bottles, 138 sticks, 67 glowstone
300 witches 10 luck
72 redstone, 77 sugar, 57 gunpowder, 68 eyes, 85 bottles, 132 sticks, 68 glowstone

results from chests was greatly seen.

1 book out of 30 and 1 chest with 2 diamonds out of 30 with no luck
4 chest with diamonds (1 had like 6), 4 with books out of 30 with 10 luck

luck 3 30 chests, 7 diamond chest, 1 book (book is rarer)
luck 6, 30 chests, 8 diamonds, no books
luck 6, 30 chests, 4 diamonds, no books
showing good degrees of randomness

Note there are other 'rare' items in the pool that are generating I havent even been counting