Amazon, even as late as 2019, seemed ahead of Aliexpress on service and quality. Something happened with COVID which seems to have permanently broken Amazon. I understand a blip, but after 2 years, Amazon hasn't recovered.
My basic problem is that if I order medicines, I want to know they're not placebo pills. If I order vanilla extract, I want to make sure it's not produced in a chemical factory with random toxins. If I buy something brand-name, I want to make sure it has that level of quality. If I buy an SD card, I want to know it's not a defective product from a manufacturing run with a forged Sandisk label. I can't do that on Amazon anymore.
That leaves fast shipping as the prime selling point, but Amazon seems to miss delivery deadlines a lot since COVID, not to mention broad ranges of products which don't do fast shipping. Fast shipping I can count on is worth a lot. Fast shipping most of the time has negative value. Most of the time I care about fast shipping, it's because I have some deadline.