Okay, with the crits making it so that your attack does 50% more damage (1.5x can just be converted to 50% more) on top of negating 50% of the enemy defense I can see why a defensive build wouldn't be that favored if crit builds are common. But because crits are determined by "luck" and "positioning" (or simply when the plot demands of it) crit build probably don't exist. Also OFC they are gonna get the rare loot, its not even surprising, in fact the writers wrote it in a way to where its expected, because the girl as a 500% luck increase so what would've been a 50% drop chance instantly shoots up to a 2500% drop (.5*50=250) and if they're not reconning it they should've at least gotten multiple of the items since they had been shown to get 2 of the same item drop.
The title of this series should honestly be renamed to something like "The Heavy Plot Armored MC Who Has Unrivaled Plot Armor and Game knowledge while Reconning themselves"
The 50% drop chance is the base rate, that would be modified by the luck of the person and/or party that killed the frog. If you assume the drop chance modified by Luce's class bonus is 2500%, you're first of all assuming that her base luck drop rate modifier is 1, and that the drop rate modifier is linear. That seems pretty unlikely.
Instead it could be something like (for example), the drop rate is modified by
LUCK_TO_DROP_RATE_MOD_WEIGHT * MIN(LUCE_LUCK, MAX_LUCK) / MAX_LUCK
so like, say Luce's base luck is 25 (since she's a jester, probably relatively high), max luck is 100 and the luck to drop rate modifier is 0.5, then you'd get
0.5 * MIN(25, 100) / 100 = 0.1 * 25 / 100 = 0.5 * 0.25 = 0.125 -> drop rate is improved by 12.5%.
Then if we factor in her 500% bonus, it'd be
0.5 * MIN(
5 * 25, 100) / 100 = 0.5 * MIN(125, 100) / 100 = 0.5 * 100 / 100 = 0.5 -> drop rate is improved by 50%.
The point is, 500% luck increase doesn't necessarily imply drop rate is multiplied by 5. In most RPG systems, base stats are used as factors when calculating derived stats like drop rates through some complex formulas in this way.