Playing a companion tank using
Sword & Board works surprisingly well.
However, when replacing S&B with a Frost Staff,
the Frost Staff loses aggro often.
The simple reason for this is a bad time setting of the Frost Staff taunt:
The CORRECT taunt setting of the
Provoke skill (S&B):
15 sec TAUNT - 12 sec COOLDOWN
Because the 12s cooldown is LOWER than the 15s taunt time,
when the taunt runs out it can be reapplied, so the tank companion can
hold aggro.
The BAD taunt setting of the
Destructive Blast skill (Frost Staff)
15 sec TAUNT - 16 sec COOLDOWN
Because the 16s cooldown is HIGHER than the 15s taunt time,
when the taunt runs out it cannot be reapplied, so the tank companion
loses aggro.
Screenshot comparison of PROVOKE against DESTRUCTIVE BLAST (German version)

The bad taunt timing even gets worse on the
Savage Instinct skill:
15 sec TAUNT - 36 sec COOLDOWN
Because the 36s cooldown is MUCH HIGHER than the 15s taunt time,
I see no sense in this skill at all, because the companion
cannot hold aggro most of the time.
Screenshot comparison of PROVOKE against SAVAGE INSTINCT (German version)