Right - but the advantage to the drone-gun is that you can hand it to a team member with really good Palming and have them shove it up their ass, then you still have a drone. Sometimes that's more viable than having a drone try to Infiltrate. I'm not knocking the Arachne, it's a good drone and there are times when it's better than a drone-gun, but there are also times when it's worse.
Oh, huh, actually, Arsenal does have rules for the Concealability of small drones! Small drones are +4 to +6 per Arsenal 102. So, yes, I think a Machine pistol drone, which has a flat +2, might be worth it over an Arachne with a +4 to +6, especially if you want to stack it with things . I definitely think a Light Pistol drone, which has a -2, has a clear niche for a concealable way to bring a drone into places.