To me, Ali Express is great for simple items that are practically fungible commodities, where workmanship and build quality aren't that impactful, and you can afford to wait a long time for it to arrive, and you can afford to receive some nontrivial percentages of those things and they turn out to be substandard or broken or substantially different than what was pictured. No matter the co-mingling issue, the same cannot be said of Amazon.
Still, I hear you – and I get your strategy for, say, athletic shoes or a new TV or maybe even a small electric appliance for the kitchen. But what about the space where there isn't a great set of discovery resources?
For example - I needed a desk lamp recently. I didn't have a lot to spend, but I thought $30-50 should be sufficient. There isn't dominant name brand in this space, AFAIK (sure, I could go to IKEA, I guess) – but it's also not a space to find many reviews on sites like wire cutter, or some gear mag, or specialized niche community on reddit, etc. etc.
So - I gambled on a well reviewed lamp on amazon... and it died within a few months - shorting and killing USB power supplies in minutes. So, I started over - and picked a different but equally arbitrary brand in about the same price range... and we'll see. But how do I research that sort of thing? I can't afford to go through these every few months...
At that point, you might as well buy from Aliexpress and cut out the middleman (for stuff you want from China).
Or drastically cut down purchases (which is what I chose).