I'd be all for Fishron dropping crafting materials, but it shouldn't be that easy to craft items. Here's one thing I wouldn't mind seeing:
Suppose the the Fishron weapons were "legendary weapons" that required not only other crafting materials from bosses or events in hardmode, but also very rare crafting materials hidden somewhere in the map/biome (1 of each rare material would spawn in each map underground or maybe even a specific biome for instance). This would also be luck-based, but luck associated with exploration and not with a repetitive action such as beating a boss. Plus, with this approach to crafting, you'd be absolutely guaranteed to get the item if you eventually explored the entire map.
By the way, I take no issue with RNG as it is in the game, but I would certainly be in favor of making items be based more on achievements and exploration rather than repetitive actions.
Perhaps I should post this in the suggestions forum as the devs work on 1.3?