Update old legendary weapons to be as dynamic as the new ones

Thematically and functionally, I really like the way the new legendary weapons work because there's real synergy between the primary and secondary attacks. I would love to see older legendary weapons be similarly interesting. I believe it's be appropriate for legendary weapons to have higher mechanical complexity; this would also allow balancing them to be on par with the top tier weapons because they have certain conditions to achieve their max potential. Here are some example ideas:

Rune Song:
Passive - passive proc makes next secondary instantly full charge

Phantom Spark:
Passive - 5% chance to summon caveling on-hit (max 5); chance increases on crit (0.05% per crit damage point)
Secondary (100 Mana) - All personally summoned cavelings fire an identically statted primary arrow at cursor location (cannot proc passive)

Soul Seeker:
Passive - Rework passive to be damage oriented
Secondary (50 Mana) - Dash forward while striking (distance/damage scales with movement/mining speed)