The ease of use of the primary version may have had a bit to do with it: five Clan ER lasers (two large, three medium), no heat, no waiting, what's not to love? (Personally I'm not actually such a huge fan, but even I have to admit that's it still a pretty convenient little package to simply run 'n' gun around a battlefield with.)
If I had a criticism, it'd more likely be the torso armor distribution (notably on the sides -- yes, twenty-six points is the maximum you can put there, but split 17/9? How badly backstabbed can I get, again?). But even that's more a bit of a "meh" deal; it's not what I would've chosen, but I can live with it.
Not sure what exactly is supposed to be the problem with the ES/FF crit placement, unless it's in fact just that the 'Mech spends 14 slots on using both. Purely distribution-wise it maximizes available space in the arms (just where I want it on an Omni that might end up playing battle armor taxi) and still leaves six slots in either side torso; I've usually found that sufficient for my own purposes.