If you increase number of lock on targets, I can't imagine that you'd manage to keep the same lock on time.
A) It's entirely possible to engage and destroy a target before lock is even acheived, let alone missiles launched at multiple targets against an inbound craft. The Romans Blunder is a good example of this. If you know where the little convoy is jumping in, you can maul an entire flight of the Loki escort with impunity in a Myrmidon with Tempests before they even have the capability to maneuver. Now apply that to an entire flight of Ballistas with Slammers, which can already do that to entire wings of much more durable bombers.
B) Longer range only helps the Trebuchet against large targets. Small, fighter size targets will still be able to evade Trebuchets entirely and with relative impunity from that distance.
C) Capship countermeasures. If you're anywhere near a capship, watch the flare(like) rain of countermeasures engulf your missile launch. If you're not, watch as any halfway decent pilot laughs at the aspect-seeking (lack of) power of the Trebuchet.
At any rate, with the coutermeasures comment, I was anticipating UEF fighters operating in support of a capital ships asset, which is where we very very frequently see them (and honesly the only place I can think of where you'd bother AWACSing the area to get a clean jump). Keep in mind that countermeasures don't care what your target was, they just care that there is a missile and that it is locked onto something.
Additionally, Treb spam would only be good against the AI. Human pilots of almost any decent proficiency simply do not get hit by Trebs because countering them is very easy if you are not a cruiser or larger.
Also good to note that most UEF ships are significantly more durable than their Shivan hypothetical counterparts. It takes more than a couple trebs to completely destroy them.
