WaterRabbit
Explorer
I'd argue that a feat that allows you to become proficient in weapons that most games do not use isn't great.
Especially since the tables in the DMG for blackpowder weapons do give the layout for who should get proficiency in them if they are a common staple of your world.
So, you are looking at getting proficiency in a weapon that is incredibly rare, and that your DM did not give proficiency for to begin with.
That isn't "real utility" that's a niche that it just happens to cover.
I don't know what point you are arguing here. Obviously if a weapon is a common staple then this feat would not apply outside of its normal use. No one is arguing that this is a great feat.
Think "Expedition to the Barrier Peaks" as an example of where this feat could be used to expand a player's proficiencies.
Otherwise, it is a niche feat that usually multiclassing would be a better choice -- unless of course multiclassing isn't being used.