Isn't this the whole trade-off with Aldi/Lidl though? You get cheaper products, but significantly less choice. Tesco has about 5-10 different lactose free milk options; Lidl has 1 option, but it's cheaper.

I'm not really sure what you're expecting. Here's an exert from wikipedia's definition of no frills supermarket:

They somewhat employ the Pareto principle when choosing which goods to offer, meaning that in most supermarkets, 20% of products on sale account for 80% of what customers buy. Therefore, they only stock the most commonly sold products.

Their business model prohibits products that don't have mainstream appeal. So that means that they're unlikely to stock tofu, lactose-free alternatives, pak choi, etc

We generally buy our common goods all from Lidl because it's significantly cheaper than Tesco/Sainsburys etc, but when it comes to outlier products, we tend to pick those up in bulk from the Chinese supermarket, Sainsburys, etc.