From what I remember, dutasteride inhibits not just the type 2 isozyme of a-5-reductase, but all of them. Most studies show that inhibiting type 2 is beneficial for hair, whereas inhibiting the others had no impact. finasteride impacts only type 2 and 3.
The main benefit of Dutasteride is not that it inhibits all 3 isozymes of a-5-reductase, but that it is a stronger inhibitor of the type 2 isozyme compared to finasteride. The downside (and why I'm hesitant to use it), is that a-5-reductase is not just found in the scalp/prostate, but other parts of the body, most importantly the brain, especially type-1 a-5-reductase.
"In addition to inhibition of DHT production, 5α-reductase inhibitors like dutasteride are also
neurosteroidogenesis inhibitors, preventing the 5α-reductase-mediated biosynthesis of various
neurosteroids including
allopregnanolone(from
progesterone),
THDOC (from
deoxycorticosterone), and
3α-androstanediol (from testosterone).
[44] These neurosteroids are potent
positive allosteric modulators of the
GABAA receptor and have been found to possess
antidepressant,
anxiolytic, and
pro-sexual effects in
animal research.
[44][45][46] For this reason, prevention of neurosteroid formation may be involved in the sexual dysfunction and depression that has been associated with 5α-reductase inhibitors like dutasteride."