What is the point of Bestial Mutagen?

The Bestial Mutagen gives you a penalty to AC and Ref, but also unarmed attacks, and an item bonus to these. The bonus to attack is 1 higher than what you could get on a level-apropirate weapon, which is nice, but the damage is really lacking after about level 4, more than offsetting the attack advantage:

  • level 4 (4.5 vs 7 damage)
    • Bestial Mutagen: 1d8, or 1d6 agile
    • Weapon with Striking rune: 2d6 or 2d4 agile
  • level 12 (5.5 vs 10.5 damage)
    • Bestial Mutagen: 1d10, or 1d8 agile
    • Weapon with Striking rune: 3d6 or 3d4 agile

Based on this Mutagenists are better off just using weapons, but Bestial Mutagen is supposed to be their signature ability. As Pathfinder 2 is one of the best balanced games I have ever seen, I am pretty sure I am missing something, but what?