As long as people optimize their characters, there will be a certain amount of "meta" mindset for the system mechanics payoff. Realistically, there needs to be at least some level of optimization in most TTRPGs because otherwise you end up with no real differentiation between characters; which can be either abused (the GM plays favorites) or boring (everyone can do anything).
As far as eldritch trickster rogue goes, it makes a decent chassis. It is definitely better in the skirmisher role than a [sorcerer or wizard]/arcane trickster with the higher BAB and added hp. However (optimizing), a dip in another class such as brawler (snakebite striker for an extra +1d6 sneak attack), ranger (Favored Enemy plus being able to use wands of cure light wounds, wands of barkskin, etc. without UMD checks), or swashbuckler (panache and some other bonuses) to regain proficiency in light armor, as well as taking Arcane Armor Training* to boost AC without suffering from arcane spell failure, will usually work better than single classing.
*- with Quicken Spell not being viable until late as a 6-level caster, there is less competition for swift actions when casting