Discover cards that cost 1 don't see play. It's hard to see why you'd want one that costs 2.
How many weapons are good at +2 cost?
After thinking about it for a while I decided they probably made it cost 2 instead of 1 so Even decks can run it. If you look through rogue weapons the only 2 even costed ones are burgle related (in standard, although I doubt Poisoned Blade changes much for wild), and it is a similarly sparse set of options for weapon buffs.
Since they clearly wanted even pirate rogue to at least be tried, they probably forced a weapon generator to even cost so the weapon synergy tribe isn't stuck with 1/2 daggers only. 0 mana would be crazy, so here we are.
0 mana would be just Primordial Glyph level of good not crazy. It would be an interesting combo activator option and could be a consideration in miracle decks.... In this form we need crazy weapon synergies to make it work and as you said even rogue has very few of those.
Also, speaking about burgle weapons... 4 mana 3\3 is far better than... 5 mana 3\2, 3 mana 1\4, 7 mana 5/2, 4 mana 2/3 overload 1....
As a burgle rogue fan I am so dissapointed with this card. At least they gave me on curve banana generator for Lilian Voss