The problem with the ISLPL is that it ends up being a bit more of a semi-generalist niche weapon due to its range brackets. In its optimal ranges, the MPL is superior damage:weight:heat, though the LPL has the advantage of damage concentration. When range bands start to open up, the LPL can play bracket advantage versus traditional short range and older big guns, but falls versus contemporary ERLLs, ERPPCs, etc. Therefore, it performs decently in its range, but its nothing game changing like the snubby. If it had a 4/8/12 range it would be excellent, and I find the derivative X-LPL the best of the X-Pulse series precicely because it can play the bracket game effectively against most weapon loadouts.
The standard LL is a reliable and effective generalist weapon with reasonable fitting costs. Its not sexy, its not high tech, but it gets the job done. My vote goes to LL.