You've mentioned this a few times, that the gladiator background doesn't represent a generalized gladiator in the D&D world, but a specific gladiator in the D&D world. And . . . that's not what the playtest document actually says. The document does say each background has "story-orientated details meant to inspire", but that's not the same thing as saying, "This is A gladiator, not ALL gladiators." Perhaps this was their intent, but if so, it's not clear (to me). And even if they did outright say what you put forth, I still think the example backgrounds ARE world-building, and unintentionally, negatively doing so.
D&D players are used to general archetypal options that define their character, classically race and class, but also backgrounds with the 2014 rules. In the potential upcoming 2024 rules, many players will customize their backgrounds, but many others will take the example backgrounds given along with their uncomfortable world-building. Games will be filled with gladiators all knowing orcish, reinforcing the already existing trope of savage, aggressive warriors reminiscent of some real-world stereotypes.