New item droprates & Encounters with Herald

So far I have had 1x drop of the mat for Ubers, seen a Herald just once, and yet to find any of the stones for the Sunder. Still all new to me so I do not know the correct names for everything yet. But I have been farming

Terror Zones, and just not coming across this Herald except for the 1st time. No stones have dropped.

Can someone correct me on this, the mats for the new Ubers are dropped by bosses and we need 1x from each?

On separate topic, the one downside to a new character? Decreases chances. For this I mean if you have a bunch of torches, odds decrease of getting one you want. Rolling GCs, chances decrease you will get a Javazon. This also means class specific Warlock items are more difficult to come across. Almost thinking if they create any new characters, drop rates of items should get tweaked. Otherwise the chances your Javazon is going to find Java gear will be just too low.

Heralds seem to pop up quite frequently from what limited TZing I've done so far.

If all you do is tele through and kill the boss then yeah, you probably won't see them. Although even that is on occasion already enough to "draw the ire".

To actually get one to start hunting you (which is kind of a misnomer, seeing how they don't hut but just stand around a screen or two away), you do need to clear a bit more. And in my experience so far, about 1/3 to half a zone should do. Depending on zone size and monster density that is.

By new uber bosses I assume you mean the ancients?
The statues for those do drop off of act bosses, yes. But only while those bosses are terrorized I believe.
Do note that you don't need to farm all 5 acts to get all 5 statues as they're not limited to "1 specific statue for each boss". Case and point, I did a few TZ

Duriel runs last night and ended up getting 2 different statues off of him.

The stones to terrorize an entire act don't require TZ farming. I've seen a few of those drop by now and they were all just off of random stuff in (non-TZ)

Baal runs and the like.
I'd assume TZ'd mobs can also drop them but can't confirm that as I have yet to see it happen (which doesn't mean it can't, haven't done enough runs to make any such claim yet).

As for the class drop odds..yeah, on shared drops (torches, charms, ..) they do go down. But dropping from 1 in 7 to 1 in 8 isn't that big of a deal I dare say as that's really just a ~14% decrease in total "correct drops".
And for those willing to trade for things, that is offset by increased average value generation as warlocks are actually good (like..crazy OP good) and in high demand so everything you get for them is higher value as compared to say "great, another druid torch..." which is now equally more rare.