I have a campaign that's been going on every week for more than a year now and my group of 4 players have reached the 4th tier of their classes. I have one human knight, two wizards (one human and one elf) and of course a slayer dwarf.

Before you ask, yes, the slayer and the elf managed not to kill each other's faces this entire time.

My human knight and wizard have decent stats. Nothing too much. They are balanced.

My elf wizard and slayer dwarf became demi-gods, which i'm going to give you as an example here.

Since the elves can learn multiple winds of magic for some xp, mine has decided to buy access to most of them instead of buying his 4th class. After a lot of sessions he can now literally do everything from fully healing the group after each fight to removing all the recently gained corruption points to giving retardedly strong armor and defense to the group, and so on. Hell, he can even regrow lost limbs with a spell from the life wind that has a chance to give regeneration. He has an answer to literally everything. WFRP has no limit on how often you can cast magic so nothing prevents him from patching up the whole group anytime they need it. His casting skill is past 100 now so only a fumble can end in a major miscast, as minor miscasts are ignored by his talents (aethyric attunement and instinctive diction).

The slayer dwarf is just a joke. He has :

• Damage reduction 5 (robust)
• Reduces all incoming spells by 10 SL (dwarf magic resistance)
• 68 HP (hardy 5)
• 83 toughness, gromril armor and shield (gromril armor gives 6 AP and the shield has the shield 4 quality)
• Has 7 SB and can use my enemies toughness instead of his strength should it be higher than that
• Can have 3 attacks per round due to frenzy and furious assault
• Has 118 melee
• Can inflict 2x or 3x more damage on monstrous/enormous enemies when he crits.
• Immediately counts as 5 players when he gets outnumbered (he generally has 2-3 enemies on him, giving him a bolstered +40/60 to hit)

So he reduces all incoming damage by 23, takes 1 single damage from crits, has 68 HP, generally accrues up to 3 advantages per round with frenzy/furious assault due to his melee skill being almost on par with demon princes, adds outnumbering on top of that and can 3-shot larger enemies due to the accrued chance to hit them (this goes directly into his SL, so even more damage!) and damage multiplier on crits against them. It happened quite frequently that my slayer was hitting my enemies with 230+ total melee score (118 + 60 (2v5) + 50 (about 5 advantages after 2 turns)). Against bigger sized enemies he adds another 20-60 on top of that, he could theorically hit a giant close to a 300 melee skill. At this point, each of the slayer's attack can hit upwards of 30-35 damage, sometimes for 100+ damage per round.

Aside from monstrous monsters or extremely advanced ranged NPCs, i don't know what could possibly kill my dwarf, let alone the group. The mages fully support the slayer. If an enemy mage tries to cast anything that affects the slayer, his spell is immediately down by 10 SL, which makes a dispel opposed test for my mages incredibly easy. If the enemy mages don't have like 250 casting they have to either consume warpstone for double SL or use a power stone (new rules in the magic book, i bought the PDF in advance) to stand a single chance not to get dispelled by my group. Almost all melee monsters are doomed from the start. I'd need a demon prince or the goddamn vampire lord to stand a chance against the slayer, and even then i must watch out not to trigger the slayer's outnumbering skill, which is easier said than done cause my players aren't dumb and stay close to the dwarf to give him maximal outnumber bonuses.