I believe anti-magic is a wunderwaffen that'll actually work. Making it mobile with a staff allows us to use it on the offensive, so we'll be as effective as we on the defence. This then allows us to convert it into something we can launch. Imagine planting one of these wands in the side of an enemy ship, into their cold tower or amongst a group of fireball wizards. They'll suddenly be unable to cast. If we can make it selective we can cast whilst they can't. This is a whole new branch of magic that is going to be (and already is) super useful, and super powerful.
I can appreciate it if you think there's some sunk cost fallacy happening here, but I believe it's worth it.
However, your suggestions of bodkins and big shields are definitely deserving of attention. I just feel they can be completed with a revision instead of a design.
There's a bunch of reasons I'm not voting for staff antimagic.. firstly, I think we've got the big prize already. We rolled very well on the production of the antimagic spell, (6,4,5), and if we roll less well, say something with a couple threes, we'll get nothing out of it. If we roll great, good, or okay on armor or something, we'll get something out of it.
So not really the sunk cost fallacy, but more that we've hit the big prize and further work will be going for the scraps.
Secondly, I don't think antimagic is some kind of superweapon. If we launch a staff at a ship, one of their sailors will just walk over, pick up the hunk of wood, and drop it overboard, or they'll keep a copy for themselves. If you mean zap the spell a long distance with a staff, it still wouldn't do much. We've rolled sixes for effectiveness twice, and the enemy can still fling fireballs all they want. Their boats aren't magic, so they wouldn't sink or anything. And we don't know how to zap spells like that, so that's two design changes to do that, and likely a revision for naval use.
Thirdly, I think a lot of the effectiveness in antimagic was in the suprise. If their heavy cavalry didn't have all-crystal weapons, we would have gotten pounded flat and lost that battle, and likely territory with it as well. Next time, even if we do hit portable antimagic, their heavy cavalry will still be capable of stomping us flat.
Fourthly, antimagic is very easy to bypass or trump. Similar to the last one, a bolt of antimagic does nothing to a longbowman, or a man in plate armor with a sword, or a cavalryman with a steel spear. Or a boat. It was helpful for the shock value and for taking away their fancy weapons, but when you take away the magic, we are left with lightly armed men wearing cloth against guys in full plate with broadswords. That isn't a good matchup.
Fiftly, we had antimagic last turn, but we did not win. We barely managed a draw, and we were fighting defensively with the suprise and shock from it being used for the first time. If we had won, there would be a stronger case for it being a superweapon, but we did not.
tl;dr: If we don't beat a 6,4,5 on the roll, we get nothing from the new design. If we roll okay on armor, we get something useful. If the enemy designs something like steel lances or ordinary flaming arrows, we lose, even if we roll straight sixes on antimagic staves.