that seems negative like "you people", as in a sterotyped grouping of a bunch of individuals, vs. just a group of people

There's a bit of overlap.

Y'all is usually positive, but can be negative "What on earth did y'all do now?!?", and "you lot" leans negative, but can be used positively "Alright you lot, lets get it done".

Tone of voice is extremely important in both examples.

> “What on earth did y'all do now?!?"

Y’all isn’t what makes that negative. It would be just as negative if you swapped in any other pronoun (you, he, she, I, it, etc).