your player level has basically no impact on droprate of sunders, and very little impact on mob HP. In general a TZ 96 area will have 20.4% more hp than a base 85 area, because its using the base scaling value of 7447 life instead of 6182 life. Monsters simply have a % of the base monlvl values for their level in a lookup table. Same with damage, defense, ar, etc. They are only a tiny bit more dangerous, they can have slightly higher skill levels on abilities and auras and so on, generally insignificant for good builds in pvm. Their drop tables tend to cap out around level 88-91 game creators- allowing the maximum base TC87 for normal mobs in the former and superuniques to drop “Act 5 (H) Equip C”, the highest possible TC. In general, if you're high enough level to be doing TZ instead of baal runs, you're already going to max out the drops.
Latent sunders have two different ways to drop, and only from heralds in both cases. They can either be a random % chance for a normal grand charm to upgrade to a unique, same roll as dropping gheeds. This works on all herald levels, and scales with your %MF, and is extremely unlikely. And in fact could be a gheeds, incredibly unlikely as that is. They also have a specific sunder treasure class added only for tier 4-5 heralds, which always drops one of the sunder grand charms and doesn't scale with %MF, and is the intended vastly more likely way to find one. And that only scales with your game playercount to reduce the NoDrop rate.