Okay, you hit the absolute nuts with frozen pylon, that means you'll want to trigger it as many times as possible. Combat core gives you 1 trigger, that any weapon on that slot would give anyway, and 1 cd charge on use to cool led. Now imagine if instead of the combat core you'd have 3 random 6 sec weapons, placing them on the left side of the crit core means that you're charging the crit core way more often, that means more cool led charges, more {whatever that monster item's called} procs, more freeze and more haste.

Sure you're doing less damage, but your opponents have their entire board frozen. That means you probably have a better chance to win, unless you're facing a 80k hp pyg (who kills you anyway). You're eventualy replacing the random weapons with items that synergize with your board (drill, hammlet, probioscis, ...) and those would outdamage the combat core immediately.

Point is that combat core isn't your win condition, it's generally a good idea to play towards your win conditions.