Remember the old version of Tau Broadside Battlesuits… i.e. 3 Battlesuits, all with S10 AP1 TLed Railguns and either Smart Missile Pods or Plasma Rifles? Deployed in multiple groups of three along the Tau back line and upgraded with Advanced Stabilization Systems (to give them Slow and Purposeful and, hence, the ability to move and still fire), these provided the backbone of most 4th/5th edition lists and truly were feared by most other armies.
With the change in points cost for Lascannon Centurions (-10 points each, plus no mandatory Sergeant tax) and the “Siegemasters” portion of Imperial Fist Chapter Tactics providing Devastator Centurions with the Tank Hunter USR, I think IF Lascannon Centurions can quite handily mimic the same tactics as the old school Tau Broadsides.
Imagine the following task force, taken from the Sentinels of Terra supplement (Imperial Fist Chapter Tactics, but allows Devastator Centurions to be taken as both Elites and Heavy support):
-4 x 3 man Devastator Centurion squads with Lascannons, MLs, and Omniscope each (three squads are Elites Choices and one squad is a Heavy Support choice)
-Aegis Defense Line with Comms Relay
-2 x 10 man Tactical Squads with Grav Cannons/Amps and Grav guns (they use Close Range Bolter Drill from Sentinels of Terra supplement instead of normal Bolter Drill for their Boltguns)
-2 x Stormraven Gunships with Locator Beacons, TLed MMs and TLed Lascannons
-2 x Techmarines with Conversion Beamers
Tactical squads go in Stormravens, come in from reserve to help seize objectives, provide extra shooting (both Grav and Bolter fire) and Stormravens provide anti-air and anti-tank support.
Techmarines attach to two of the Centurion Squads (gaining both Tank Hunter and Slow and Purposeful for their Conversion Beamer shooting) and all/most Centurions set up behind the Aegis line for built in 4+ cover saves to supplement their T5, 2W, and 2+ armor.
Now, if you compare the TLed Lascannons (S9 AP2) on the Centurions with the oldschool TLed Railguns (S10 AP1), at first they seem quite wanting. On clsoer look, against infantry the only advantage the old Railguns had is the ability to double out T5 units and the ability to wound Wraithknights/Wraithlords on 2+ (vice the 3+ from a Lascannon). Otherwise, the BS4 Centurions are more accurate, wound pretty much all non-vehicles on 2+s, are tougher than Broadsides (T5 vs T4), and have better leadership/staying power with ATSKNF.
Against vehicles, except for the AP1 factor, Lascannon Centurions with Tank Hunter are actually better tank hunters than Railgun Broadsides of yore.
Against AV12 tanks:
-A squad of 3 Sentinels of Terra Centurions with MLs and TLed Lascannons shooting at 48″ gets 3 lascannon shots/3 krak missile shots, 2-3 lascannon hits/2 krak missile hits, and 3-4 stripped hull points
-Comparitavely, a team of 3 old school Broadsides with TLed Railguns and TLed Plasma Rifles shooting at 24″ got 3 Railgun shots/3 Plasma Rifle shots, 2-3 Railgun hits/2-3 Plasma Rifle hits, and 1-2 stripped hull points.
Against AV 14 tanks:
A squad of 3 Sentinels of Terra Centurions with MLs and TLed Lascannons shooting at 48″ gets 3 lascannon shots/3 krak missile shots, 2-3 lascannon hits/2 krak missile hits, and about stripped hull points
Comparitavely, a team of 3 old school Broadsides with TLed Railguns and TLed Plasma Rifles shooting at 24″ got 3 Railgun shots/3 Plasma Rifle shots, 2-3 Railgun hits/2-3 Plasma Rifle hits, and about 1 stripped hull point.
As you can see by the Mathhammer, Tank Hunter Centurions (i.e. Sentinels of Terra or Imperial Fist variety) are measurably stronger against vehicles than the old Broadside teams.
Combined with the Aegis Line and T5 for enhanced survivability and adding in Conversion Beamer shooting from the Techmarines and the fire support from the Tac Squads/Stormravens, I think you can produce a very effective, shooty-focused Sentinels of Terra list built around a foundation of Lascannon/ML Devastator Centurions.