Mar, I'm going to have to disagree with you here. I'm by no means a dropshipping guru (you can read my dropshipping story here:
https://forum.alidropship.com/threads/and-heres-mine.4567/ ), but I have many years of experience in a related branch.
The advantage of a niche store is that you're attracting people interested in your niche, who are more likely to buy. When you try to think like a potential customer, ask yourself this: Say the customer is interested in cat-related products, do you think he's more likely to walk into a shop selling only cat-related products, or to the flea-market where you can buy anything from a roll of barbed wire to a 2nd-hand police uniform? The customer doesn't want to be distracted by other things, he wants to see products related to cats.
It's about quality of traffic, not quantity. If I sell cat-related items, I don't want a customer in my store who is actually looking for a power-drill, then sees a nice little cat-collar bell and buys it on impulse. I want a customer who comes looking for a bell for his cat, and then sees that I have a few different ones to choose from - he's way more likely to buy it. Of course impulse buying exists, but that is where you can use AliDropship's upsell and cross-sell feature.
As you can see from the stats of my two dropshipping stores, I get very little traffic, yet I get sales. On both shops I had my first sales within the first month. That's because I target my customers by niche - they come there because the niche excites them, not because there's a store that sells anything under the sun and they hope they might find something they need or like.
Focusing on a niche also focuses your marketing efforts You need to really understand the niche to be able to think of the proper keywords to use, the proper language to use when you market it. You have to know WHY your potential buyer is interested in cat-bells. Does he just want to know where the cat is hanging out, does he think it's cute, or does he want to put a bell on his cat to warn birds that they're about to be eaten? If you get it wrong in your product description, you lose the buyer's trust, and he goes to a different store where he thinks the store-owner actually knows what he's talking about.
Niche is also about SEO. Many people seem to think that it's all about Facebook or Instagram to get your customers. Whereas proper SEO costs you nothing, and is way easier when it's focused on one niche. Google will give your site a higher score if the Google spiders see that your store name, content and meta tags are all about the same thing.
Finally, imagine that your store becomes really popular and you start getting millions of visits per day. If your store is tightly niche-related, you'll be getting few visitors, but a high proportion of them are ready to buy. With a general store you'll be getting a huge volume of people just aimlessly browsing around, with just a small proportion of them buying. This will necessitate upgrading your hosting, because it will slow your site down, and you'll exceed your bandwidth allocation.