All three Point Defenses are almost identical. Same DPS, same health, same cost. The Illuminate Point Defense has a range of 45 instead of 40, giving it a better range by 13%. The UEF Point Defense has a rate of fire of of 1.5, whereas the Illuminate and Cybran Point Defenses have a fire rate of 2. Even though the Cybran is labelled to be "Rapid Fire", it fires just as fast as the Illuminate Point Defense until the Rate of Fire research is completed, at which point its DPS becomes superior.
The UEF Point Defense fires in a low arc, allowing it to be more effective on un-even ground.
It‘s worth noting UEF PD isn't built to be a "stand alone" weapon, but is meant to pick off units already damaged by Light Artillery Station shelling first, which may explain the reason why they are so weak, however it upgrades its health more than the other two PD do.
With Rate of Fire the Cybran Point Defense can increase it's fire rate by 30%. This is multiplied with the damage improvements granted by Training and Veterancy, potentially giving a single tower 585 DPS with full training and no veterancy, and 780 DPS with both maxed.
The Illuminate Point Defense has a +10% damage tech. It can also hunker and has a personal shield, equivalent to 20% of its base health.
The UEF point defense does not gain any damage bonuses, however, the UEF have research abilities that turn their Mass Extractors and Research Stations into point defenses. So while the UEF Point Defense is the worst, the UEF are usually the best defended with Point Defense like structures. UEF point defense should be backed by Fortified Artillery, which can be turned into area affect PD with the Hardened Mode ability. Also, UEF Energy Generators have the Engineering Tower upgrade which pretty much gives them an engineers arm to repair or complete construction of things within range.
If a ranking had to be made, overall, the Illuminate PD is best due to its toughness and range, followed by Cybran for its raw firepower once upgraded, then UEF. The Illuminate PD deals the same amount of damage as the Cybran but with longer range and the ability to mount shields and hunker, and the Cybran deals more damage than the UEF PD while having the same range. UEF point defense deals less damage than the other two, and has shorter range than the Ilumminate PD.
Point Defenses should not be relied on for more than an emergency slowing measure or to ward off opportunist raids from assault bots. They become obsolete once Mobile Missile Launchers come on line. They regain some value once backed up by shields. if enough shields are placed with enough point defneses they CAN stop just about any attack if backed up with long range support or air support, that can be used to knock out any long range arty fire. 5 upgraded geminis can stop a fat boy in 2 runs and 3 to 6 shields placed behind the defensive line kept the fire well suppressed.
Point Defenses are key to an offensive "Firebase" oriented strategy.
Placing Point Defenses in pairs around the map can stop engineers from spreading Mass Extractors everywhere.
They are useful as well for preventing engineers from converting your remote Mass Extractors.
Because of the range of the Illuminate Point Defense, It can block the other faction's "creep" strategy and can be used for the strategy as well.
Use long range units to suppress point defenses. If that is not possible, due to enemy artillery or lack of available units, have your assault teams keep moving as they attack the towers. This forces the towers to constantly switch targets, making them far less effective. Constant moving also keeps you safe from incoming artillery fire.
Against the AI, point defense seems like highly effective base defense. Don't be fooled into thinking that human opponents will send their tanks to the slaughter so easily. But most times they will.
For the price of a single tower, remember that it is possible to buy a number of ground units instead which is often more useful due to their mobility.