I tend to drive either Lights or Assaults, so XLs are either a must have or must NOT touch thing. Assaults, too often I don't die to the guys shooting at my face, it's the little bastiches who snuck up behind me that get me, and an XL in an Assault means I don't even have a chance to turn around after the first shot into my ass. Without an XL, well, I'm one of those people who just doesn't get the entire lagshield thing, I don't have problems putting AC/gauss rounds into Lights, I just have to get the chance to SHOOT at them first, no XL gives me that chance
My Lights, well, I'm the bastiche sneaking up behind Assaults firing into their ST rear armor to check for XLs
With the quirks being added, there are some Mechs that could actually get away with an XL, but I just can't make myself build to the quirks yet. For one, I think they are WAY overboard for the IS which means they'll get nerfed at some point, so why make a build that I KNOW is only useful until the next patch? Look at all the screaming about real money, cbills and time spent getting TBolt 9S's all Mastered out before they requirked it, no thanks, I'll avoid that bs totally and just build my Mechs the way I always have. I like certain weapons, regardless of what the meta may be today or tomorrow, they work for me, so I use them. Certain Mechs appeal to me for whatever reason, so those are what I use and that's what I have fun in.
Meta right now in MWO is a funny thing, it's not about what really works, it's about what's the most OP currently, and it changes constantly, so I avoid it at all costs.