It's in a weird place because it's "OP" in social encounters, not combat encounters, which makes it harder to quantify. Think of it this way: being able to change your appearance (and in so doing potentially mimic the appearance of another person) is the effect of a 1st level spell, Disquise Self. Not only is the Changeling's ability significantly more powerful than Disguise Self (it holds up to touching, can mimic your voice, is unaffected by anti-magic effects, unlimited duration) but your uses of it are unlimited. In effect, this is giving you a more powerful version of a 1st level spell at will. Other races get first level spells as racial features, but IIRC none of them get the effects boosted and all of them have the spell limited to 1/day.
Changling shapeshifting also doesn’t change their clothing, which severely hampers what they can do in a pinch. They can’t just turn a corner and adopt a completely new appearance at will, like any second level Warlock can.
And, every race should have something that makes them stand out, and have aspects of the game where they naturally shine. The Changling has that, but only in the hands of a very Hand-wavey DM will it break the game, bc they still need costumes, and they still have to use Deception to change their voice, and they still need time to actually change clothes.
By the time they have magic items that can alleviate those issues, other characters can cast disguise self several times a day, if not at will.
Meanwhile, I don’t know if you’ve ever DMed for a wood elf and lightfoot Halfling stealth specialists, or a gnome rogue, Paladin, or ranger mage slayer build, but I assure you I can make a DM work harder with those characters than with a changling.
Changling s are a tier 1 race, for sure. IMO post PHB tier 1s always get called OP, even when they aren’t, because we’re all gun shy about power creep. But they aren’t broken.