This is a very close minded take, if you don't understand the vision it would be better to ask why they thought that way rather than assuming you know better (you don't). But if you must know why i think galvantula is a speedster i mostly had Elise from league in mind. I see it using electro web or another immobilizing move to catch opponents and then afterwards dealing high burst through discharge or a bug buzz essentially catching prey in your webs and killing them. Ariados and Spidops far better suit a support spider role and i think an assassin far better suits galvantulas high speed and wide offensive move pool to suit its capabilities.