For the playstyle ? I like nimble melee dps. Sure I have to work far more for my dps than a warlock or ranger but I like it
Plus at level 4 , rogues deals quite some heavy damage.
But sure you can play without a rogue ,just as you don't need a druid or ranger or a mage necessarily. On the fair side , having a specialized stealthy lockpicker , skilled at pickpocketing can be appreciated just by the fact the rogue will be in charge of having skills to make it easier while your warlock ,who is limited in skills to begin with , will focus on 'conversation' skills (at least that's what mine does).
Yeah, playstyle, mainly. My first run through was a rogue, I'll explain that in the next mini-paragraph. I love the skills. Like a lot. But they're pretty useless in combat, unless they're ranged, at least in my limited experience.
It gives me no joy to say that, honestly. Through EVERY DnD game I've ever played, I've pretty much played a halfling rogue, human bard, or a wizard. I don't think I've ever played a warlock.
Perhaps changes will be made.
