I have been testing the 2H Ultimate, Berserker Strike and its morphs in PTS.

Here are the results -

Stats
Weapon Damage : 4301
Stamina : 33912
CP : 561 (100 in mighty, 70 in precise strikes)
Mundus : Shadow
Tooltip : 16346 damage

Test 1: *3237* blocked
Test 2: 13390 critical
Test 3: 7969 normal
Test 4: 2167+6001 against shield
Test 5: 9178 empowered normal
Test 6: 17689 empowered critical
Test 7: 11657 empowered critical
Test 8: 9345 empowered normal
Test 9: 9987 empowered critical
Test 10: *3978* empowered blocked

I tried the move a total of 50 times, those are 10 randomly picked from the 50.

Average normal hit - 7500 (approx)
Average critical hit - 12500 (approx)
Average blocked hit - 3300 (approx)


Now, my stats are not that great and it is possible to get 20k and more tooltip for the hit. Due to the fact the ultimate ignores mitigation allows it to hit very close to the original tooltip with a normal hit, or half of the tooltip with Battle Spirit. However, it is close range and dodgeable as well quite easy blocked.

Advantages without morphs:

• Very strong burst, in fact over 12% stronger than Incapacitating Strike without even considering the fact that it ignores resistance and also at least 40% stronger than Dawnbreaker's initial hit without considering the fact that it ignores resistance.
• Quite fast animation and hence can be a bit hard to realize.
• Ignores resistance.
• Steals enemy resistance.
• Not very extensive.

Disadvantages

• Easily dodged and susceptible to Major Evasion.
• Hits like wet noodle against block.
• Not AoE like Dawnbreaker and no DoT.
• No CC attached.

Unlike my previous posts, after testing it, it does not feel as broken as I first assumed.
In my opinion, till this point it's still not OP.

However, it's the morphs that makes it broken.
Berserker Rage gives you free CC immunity to both hard and soft CC for 8 secs.
Onslaught returns the entire ultimate cost, if it kills an enemy.

These morphs tilt the swing way too far. My stats used are pretty low as mentioned before as it is possible to attain 6k+ weapon damage and 40k+ stamina resulting in crazy damage, even reaching one-shot capabilities in certain conditions.

How it can be balanced (some small change suggestions)

Berserker Rage: The tooltip damage of the morph gets decreased by 30%. But the ultimate can hit for upto 100% more as the user's health goes down. If used successfully when under 50% health, gain immunity to CC, snare, immobilization and disabling effects for 8 secs.
Explanation: This morph will give a risk and reward sense to skill. It will generally hit lesser harder than the unmorphed skill but if the user is under around 30% health (basically execution range), the ultimate will start hitting harder than the original skill. If it successfully connects, it will also give CC immunity. This will allow the skill to be used in a defensive-offensive nature at a huge risk of missing and/or getting killed in a single hit and also losing 150+ ultimate which could have used for purely. If it hits, it will give the user a chance for a comeback from very bad positions, but it fails it nearly guarantees the user's loss.

Onslaught: If this skill kills an enemy, 50% of the ultimate cost is immediately refunded and Major Heroism is gained, giving 18 ultimate in 8 seconds.
Explanation: This one is simple. Instead of returning the entire ultimate cost as it does not, it will return 75 ultimate and 18 more ultimate over a span of time. Far more balanced than random spamming.

Of course, unless the patch goes live, the true power of the ultimate can't be judged. Often many seemingly powerful things on paper can turn out weak in real use, which will be tested after the patch goes live. But, something things like refundability of the cost of a powerful skill lies too close to crossing the dangerous line of balance. Which is why I placed my suggestions here.

@ZOS_GinaBruno , @ZOS_KaiSchober , @ZOS_RichLambert , @Wrobel , @ZOS_BrianWheeler , @ZOS_Finn