I play in two worlds. In the first I am in a small guild and level 5 won't be unlocked at all because it is too expensive while there's no one interested in doing it.
In the second world level 5 was unlocked, so I gave it a try. Encounter 1: The first attempt was a failure; the second was a costly success after I built a fortification increasing the Attack of my army by 20%. And all I got in return were a measly 10 Fragments.
Encounter 2: I gave up after killing half of the first wave of enemies because I determined that I would lose too many units during the second wave – totally not worth it just to get some fragments from another building I don't need.
Overall level 5 is NOT WORTH IT unless you can do at least 12 of the 16 encounters. In the future I will either avoid it completely, or do only the very first encounter.
Some more general feedback:
It makes no sense to have the first four levels use Attacking army stats, only to then switch to Defending army stats.
You want to add a fifth level to GE? Have it use Attacking army stats, same as the previous four. Players would be a lot more accepting of the ridiculous enemy stats in this case.
Want to use Defending army stats for something? Create a NEW addition to the game – let's call it Fragments Hunt because of all the fragments – and give it five levels, each level more difficult and challenging than the previous, but have it start with low enemy buffs – or even 0% - similar to how GE levels start low and gradually grow. This way players will be able to see their progress as they increase their Defending army stats, and will also have a lot more reasonable goals.
Again, the current iteration of GE level 5 is NOT WORTH IT – the cost is too high for the trash prizes we can win.