*shrug* counter-counter point. Absolutely zero RAW on how dispersed your SWARM has to be. Total GM fiat. Also no RAW on types of Drones needed to SWARM. You could have Kanmushi's in the vents, Flyspy's zipping around, and a Rotodrone with a Sniper Rifle parked outside that doesn't care about walls. All up to the GM to adjudicate how that works.
Counter-Counter point #2, grenades are obviously a combat response. Your Swarm should have been rocking 29ish dice Sneaking and should have been undetected until they opened up and turned most of the field into a hellscape of flashbangs, Thermographic Smoke, and suppression fire.
Counter-Counter point #3, don't forget Social skills can all be defaulted to! Take your Realistic Features 4 Anthro Drone, stick it in some Mortimer's, slap on a little Black Panther, you're rocking 20+ Dice for that Negotiation test. Matrix skills, also possible to default to several of them, which is a path to darkness I've never bothered to figure out. But theoretically possible to build a gang of Agents and Drone Swarms doing all kinds of stupid.
Drone Swarms and Sustain mage builds can totally disrupt a table and steal from another player's spotlight by completely blowing the other PCs dice pools out of the water. Overdrive isn't going to do that. TM w/MBW and Machine Sprites can certainly do some clever stuff, but can still be outdone by specialists and have some significant compromises to deal with. The TM w/MBW build has been around for a long time, Overdrive at best adds a couple dice to those shenanigans.