Dollar Tree has essentially always been like that. It was never really there for "deals" because of what you mentioned. Usually the items were just smaller packages of things which is why they cost less to begin with.

But it has always been fantastic for certain kinds of items:

1. Birthday/greeting cards. They are always simpler and of lesser quality than at other stores. But is anyone really going to keep your card for a prolonged period of time? If they do, it's probably because of what you wrote in the card to personalized it, not because the card was fancy. I've seen greeting cards go for up to $10 in some drug stores which is pretty wild to me. Yes, they are more elaborate, but does it really matter when the cheaper one suffices?

2. Gift bags. Same dealio as above.

3. Wrapping paper in very particular circumstances. They have significantly less wrapping paper in the package than at other stores. But I find sometimes it's a good thing if you only want to wrap a present or two with that style of wrapping paper. If you want to wrap many things or if you want to use more of the same paper in the future, then I'd buy elsewhere to get a larger quantity.

4. Letting kids pick out some cheap crap from the toy aisle.

For basically anything else, it's not worth it imo. But the above have always been where it shines.