Snap's UI is horrendous and it has nothing to do with ads. Kids can invest innumerable hours to find and utilize all the hidden ways to interact but your average adult is just going to do the basics and will put it down.
That's fine. Kids are often the market these social media companies target as they launch anyway.
At least software that ran in a text based terminal would customarily come with a manual.
Snap is a lot like that magic bag in Harry Potter that was bigger on the inside. You never knew what was in there till you stuck your hands in and hoped for the best.
Instagram has a pretty craptastic UI itself. It's a pain in the ass to copy images from the web UI (Have to use the inspector to get the link) and the video player doesn't let you skip ahead or move back.
I'd agree if those tasks were part of what they were planning to be a part of the app experience - but seeing as they're explicitly not, then from a pure design perspective, the UI is perfect in that regard.
It's bad, but bad intentionally. I haven't noticed it being buggy like snap chat. They just went out of their way to break features the browser gives you for free.