Yes, in a desperation situation you can certainly send out Sidhe with just their base equipment and after they buff they'll do ok, but there's a big difference between having a 99% chance and having a 90% chance. The properly equipped guy is almost infinitely reusable unless you hit a mage supported defense, while the lightly equipped guy will probably take out a couple provinces but he'll very likely pick up an affliction here or there and shortly get one which makes him useless as a raider if he survives the fight. Also, your opponent can counter him with sufficient PD whereas the vine shield guy can take pretty much an unlimited amount of PD. Plus, lets be honest, you're not really gonna rectify the omission, that's just something you tell him. There's always another Sidhe popping out the castle to give the vine shield you just made to.
