I dunno, the Prism seems to be the superior choice against horde-guard simply because they can kill much more of them from much farther away.
Your right that Falcons are better at killing MEQ's (2/1.61 Star Falcon/Scat Falcon vs 1.11 Prism), and they also kill light vehicles better, but Eldar have units that already fill in those roles quite nicely. However, Prisms are solid anti-horde/heavy vehicle units (Prisms are superior against infantry models until you hit either T5 or 3+ save models and become superior against vehicles at AV 13).
If I got my math wrong, please correct me, but here's something I threw together in excel:
Code: Select all
Assumptions/notes:
Blast marker covers 2 infantry models / 1 vehicle model
Large blast marker covers 5 infantry models
No bank shot
Range to target is between 12" to 36" for the Falcon, 12" to 60" for the Prism
Star Falc = Starcannon Falcon
Scat Falc = Scatter Laser Falcon
Prism = Fire Prism (focused shot)
Disp = Fire Prism (dispersed shot)
Avg failed saves (armor & inv only) & unsavable wounds
T Sv (++) Star Falc | Guide | Scat Falc | Guide | Prism | Guide | Disp | Guide
3 5 0 2.00 3.00 2.39 3.58 1.11 1.48 2.78 3.70
3 4 0 2.00 3.00 2.00 3.00 1.11 1.48 2.78 3.70
3 3 0 2.00 3.00 1.61 2.42 1.11 1.48 0.93 1.23
4 5 0 2.00 3.00 2.39 3.58 1.11 1.48 2.22 2.96
4 4 0 2.00 3.00 2.00 3.00 1.11 1.48 2.22 2.96
4 3 0 2.00 3.00 1.61 2.42 1.11 1.48 0.74 0.99
4 2 5 1.33 2.00 0.94 1.42 0.74 0.99 0.25 0.33
5 2 0 1.83 2.75 1.06 1.58 1.11 1.48 0.28 0.37
6 3 0 1.67 2.50 1.28 1.92 0.89 1.19 0.37 0.49
6 2 0 1.67 2.50 0.89 1.33 0.89 1.19 0.19 0.25
7 2 0 1.50 2.25 0.72 1.08 0.67 0.89 0.09 0.12
8 2 0 1.33 2.00 0.56 0.83 0.44 0.59 0.09 0.12
Avg # Penetrating & Glancing Hits (no Guide):
Star Falcon Scat Falcon Prism
AV Pen Glan Pen Glan Pen Glan
10 1.00 0.50 1.33 0.83 0.56 0.11
11 0.67 0.50 0.83 0.83 0.44 0.11
12 0.33 0.50 0.33 0.83 0.33 0.11
13 0.17 0.17 0.17 0.17 0.22 0.11
14 0.00 0.17 0.00 0.17 0.11 0.11
As for their transport role, the only time a Falcon would be more useful than a Serpent is if your transporting Harlequins, since the change to Spirit Stones means that you can pretty much write off any Eldar transport's shooting capabilities if you're actually planning on using them to transport a unit.