Sebum does have its good and bad. Too much of a good thing is indeed a bad thing. In moderation, it helps hair by keeping it moisturized and healthy, also protecting it from outside debris and pollution, yet too much will create an environment suitable fo hair loss..
About 5AR Type 1, i am honestly on a fence here. Obviously it still synthesizes T to DHT, so it can be considered "bad" for the average balding joe, yet it also exists in considerable amounts in the brain and liver (as opposed to Type 2).. which surprisingly, only recently that dutasteride was found to be linked to higher chances of diabetes, higher cholesterol, NAFLD / liver enzymes and insulin resistance. It may have been due to its inhibition of 5AR Type 1( which again, exists in considerable amounts in the liver).
If scalp sebum problems are very severe, Nizoral could help quite alot, or better yet, even low-dose Accutane would pack a punch and has higher rates of success than solely relying on inhibiting 5AR Type 1, but that might be just me.