Fin/Dut are irreversible competitive inhibitors of 5-AR. Let’s say that once a particular 5-ar enzyme becomes part of the aforementioned covalently-bonded 5-ar+NaDP+Fin/Dut complex, then it is permanently inert.
For the remainder of its existence, the active site is blocked and it will no longer act as a catalyst in the reaction of T + NaDPH -> DHT + NaDP+ and it will eventually be destroyed by the cell’s waste management systems.
Meanwhile, new 5-ar enzymes are being produced and if fin/dut is present in appreciable concentrations, those new enzymes will share the same fate. If no fin/dut is present, they will catalyze the reaction of T + NaDPH -> DHT + NaDP+
More discussion about the mechanism of action of finasteride here:
Not going to go into a lecture about seeing the forest for the trees, but the result of taking fin or dut is a reduction of DHT and some other products of 5-ar metabolism. Either drug could work by sucking 5-ar into another dimension on a molecule-per-molecule basis and the result would still be the same.