I have set my Boff skills up to use cannon / torp skills, shoe horning a beam array into my setup would lower its efficiency due to either leaving the beam array with no boff skills to enhance it or replacing a cannon skill reducing the output of my 4 remaining cannons.
Either way being forced into using a beam array would lower my overall damage output and it seems endgame is all about max DPS.
Honestly I'm finding I like having this single beam weapon on the front of my otherwise cannon Tor'khat. It gives me better damage against targets not yet in the cannons' arc, and the 3-piece ability works like overload + debuff and is nice as an opening shot before the cannon bolts start slamming in. Having a weapon with zero drain doesn't hurt either, since it ultimately boosts all other damage as well.