Draztal
Der Thron des Donners normal isn't tuned assuming you are a Heroic raiding guild. If your raid is still progressing through Tier 14 (say, at Garalon) it's very likely you'll be able to only kill
Jin'rokh der Zerstörer and then face a very difficult battle trying to slay
Horridon or Council of Elders, though.
In that case (and for the guilds still progressing through T14) it probably makes more sense to go back clear the rest of Tier 14 (which is now more doable thanks to the 10% reduction in damage and health of bosses as well as the new VP gear you can get with 5.2 Patch).
Guilds that have completed Tier 14 Normal already should be able to progress through
Der Thron des Donners. Of course, you might not clear all of it in a couple weeks, but it's something definitely doable without getting Heroic gear from Tier 14 (gear from Normal Tier 15 is higher item level).
On the other hand, it's also important to keep in mind that
Jin'rokh der Zerstörer is a rather easy boss. He's not necessarily a representation of the rest of the raid's difficulty. Which is something many of you have probably noticed while progressing on
Horridon or Council of Elders. And that might set a wrong expectation as to how quickly you can/should progress in
Der Thron des Donners. It's very possible to kill
Jin'rokh der Zerstörer without much difficulty and then suddenly feel like
Horridon is a brick wall, don't despair!
There are many encounters in
Der Thron des Donners that your raid will have to learn. And it's normal to feel things may be overtuned at the beginning of a new raiding tier while everyone is trying to better understand what each boss does and how to execute the fight properly.
Not everything comes down to how much gear your raid has. In fact, you might overgear, say,
Horridon, and yet be unable to progress past him due to an inefficient strategy.
In any case, the developers are keeping an eye out on how things are going, and they will be making adjustments as needed. Ideally, no one should find him/herself in a situation where it looks like it's impossible to win without getting more gear and unable to actually get more gear.
So, don't give up. Go get those
Tapferkeitspunkte items (some items from Raid Finder might help as well, absolutely) and keep refining your strategies. The boss kills will come :)
It's definitely true, however, that jumping from Garalon to
Der Thron des Donners might be stressing for the raid group on the first weeks. As the raid gets more gear from the newest Raid Finders, the 5.2 Valor Point items and so on, they'll start progressing through the harder encounters.
But, even if you start making progress past
Horridon and Council of Elders, I'd honestly encourage you to go and finish
Das Herz der Angst in Normal, and
Terrasse des Endlosen Frühlings.
Terrace is particularly useful as it drops 2 tier pieces, Sha-Touched weapons and it has minimal trash, which means you can clear it in around two hours once you get used to the raid :)