It's just a result of the design philosophy of the Clans as opposed to the Inner Sphere, and how each approaches warfare. The inner Sphere builds for flexibility and speed, and so if speed is your primary concern, then a mech from the Inner Sphere is what you will want to pilot. The Clans build for firepower first, last, and always, and if this is your concern, then you should pilot a Clan mech. In terms of survivability, they are about even, with the Clans having a one-tech XL engine that allows survival with penalties, while the Inner Sphere offers either survivability without penalties (standard engines) or complete vunerability to serious damage (XL engines).
In terms of light mechs, this translates to Clan mechs not really being built with speed in mind, but with the ability to seriously damage or destroy anything it comes up against. As long as the mech has the speed to keep up with the rest of the Star, then it is considered all that is needed. Inner Sphere light mechs, by comparison, are designed with the idea that speed is a priority even at the expense of firepower.
Remember, the Clans designed their mechs for single combat warfare, so consider how well an Inner Sphere light mech would do in a restricted arena battlefield against a Clan light mech, with no other mechs to assist.
At the current time, this is simple choice by the pilot of what they want at any given time, picking the Inner Sphere light mechs when they want speed, and the Clan mechs when they want firepower. When/if Faction restrictions are put in with CW, then the Clans will simply have to accept the Clan way of warfare, and the Inner Sphere theirs, with all the advantages and disadvantages that come with their choice.
Edited by Jakob Knight, 26 June 2014 - 02:47 PM.