It doesn't have to be the same player, planeswalker, or battle that Arthur or any other attacking creatures are attacking
This is strongest in the mid- to late game, acting as a counterspell that gives you a mana boost
The big question is whether those upsides outweigh the things you lose by dropping white
However, as a card drawing engine, the Sword is barely better than Rogue's Gloves
Though its a do-nothing card in many decks, Commanders like Hearthhull, the Worldseed turn it into a terrifying ramp piece, and sometimes even a finisher
owyn, Fearless Knight Handling big threats with style, owyn, Fearless Knight exiles a high-power creature when it enters and gives your legendary team protection from that creatures colors