Maybe it's my own local meta, but as a medium mech I don't often see the Trebuchet on the table, outside of running it in my own Dogs of War mech company lances.
For around 1200 battle value it is a bit high, but among other mechs in its class it has something very valuable- redundancy. We start off with the two LRM 15 launchers. I prefer LRM 15/20 just for the volume of missiles, I feel like if one is going with a LRM 5/10 perhaps an AC is better.
Two 15 packs means two shots a turn, and most times one will hit, and if both hit due to lucky dice or correctly controlling the movement and cover modifiers that is some good damage going down the table. Next we close with the 3 medium lasers- three chances to hit, solid constant fire- more redundancy.
I find the Trebuchet an excellent support mech (as it's intended) which advances and lays down the missile smack before closing an firing the medium lasers- works as intended when it is paired with another mech or two.