I was in two minds whether to post this here or in Why hate piranhas? viewtopic.php?f=52&t=24307
In the end I decided it belongs here.
Reflecting on why I was so happy with some of the units I took to the GT last month I began to realise that the way they work together is the key. I have done some number crunching on this to understand how much their performance has changed since the 6th Edition codex.
What I started looking at is the efficient delivery of pulse firepower to the enemy, S5 AP5 massed firepower is effective even in the current meta provided you deliver it in a cost efficient manner. If we look at just the basic units that are unchanged from 6th without formations and look at the points cost per average hit at optimal range we get
9 Strike Team
9.4 Crisis suit, TL BC + BC
9.5 Piranha + drones
10.8 Gun drone attached to Crisis Team
12.6 Gun drone in drone squadron
15 Stealth Team
So the classic Fire Warrior was the gold standard of pulse firepower and anything resembling a pulse bomb was going to start there and begin augmenting them. Crisis suits are good but get less efficient when you add drones, Piranha were pretty decent but do not benefit from a key augment (an Ethereal) as well as Fire Warriors and took up a Fast Attack slot needed for the other source of augments: markerlights.
When you put a Drone Net VX1-0 on the table things change
8 Piranha + drones
8 Gun drone attached to Crisis Team
9.3 Gun drone in drone squadron
What has happened is that before any further buffs the Piranha has become better than the previous best source of pulse firepower. When I combined this with the mobility of being in a Hunter Cadre and the effective threat range of 42" it is hardly surprising I found it so good. It is worth noting that the Drone Net gun drones themselves are almost as good as the previous best on a point-for-point basis and have a handful of fantastic special rules to make them even better. The Drone Net itself is certainly not a tax.
So this made me think about looking at what other options around this there might be. The synergy with the Piranha Firestream was obvious at first glance so I started looking there. Lets look in a different order this time, at some scenarios of using the formation on the table
8 Piranha + drones
7.1 Piranha + drones using the BS boost from the spotter
5 Piranha + 4 drones on turn 2 after one Refuel & Rearm
4.6 Piranha + 4 drones on turn 2 after one Refuel & Rearm using the BS boost from the spotter
5.6 Same as above but without the drone net
So what we now have is on turn 2 a unit that before any boosts is pretty much twice as efficient as the previous gold standard of delivering pulse fire to the enemy. This is highly impressive firepower efficiency and anything coming inside our deployment zone on turn 2 had better be near-immune to pulse fire or it is going to get swept away. Unlike the old Fire Warrior version of this we do not need to add more points to make it mobile; Piranha are mobile already and the detached drones are respectably quick around the table.
That the key to all this is merely having a Drone Net on the table is why I posted it in this thread. Without the Drone Net it loses over 20% of its efficiency and if you are going to invest in this a 20% better return on your points really matters (you need the markerlights anyway so its still not a tax). I think the massed pulse fire build may be viable again and what makes it viable is the Drone Net, combined with the Piranha Firestream.