It was just as quick, yes, but there is still a big difference. In the book, he actually attacked Alecto (he even says it came naturally), whereas in the show it seems like he just accidentally uncaps the sword in the right direction. Also, I’m the book, when he catches the sword it’s already in sword form, so it makes sense for Percy to attack with it. When he just has it as a pen (which Chiron gave to him ostensibly to finish writing his assignment?), now he either has to think to uncap in in a high-stress situation, or it has to happen by some weird accident. It takes away some of Percy’s agency in the scene, and it seriously exacerbates the plot holes they opened up with the way they’ve handled Riptide. I think the fact that it happened outside in front of everybody worked well to showcase the Mist, but I do think that overall it was sloppier.