For one thing, cheap lights rarely have good color rendering. They make people look like zombies, wash out detail, and just don't do color very well. If you cannot tell brown from green, you will step in that dog mess in the lawn. While some enthusiast-grade lights also do that, most enthusiast lights that lack color rendering make up for it with sheer throw. Often in the 400-800m range, and sometimes up to 2,900m (yes, ~1.8 miles).

As for "similar brightness", a lot of cheap lights do not meet their claims while enthusiast lights do. For instance, the light you see sold a lot under hundreds of different names (including Gearlight S1000) and many of us get a cheap knockoff free with our battery orders claims 1,000-2,000 lumens depending who slaps their name on it, but it actually doesn't even make 300. The D2 gets about double that at startup. On one channel. Oh, and if you zoom that Gearlight to max throw, it's only 86 lumens; about half of what a D2 can sustain for the entire charge of it's battery. Here is what a 1,400-lumen light that *actually *makes 1,400 lumens looks like. And both the D2 and TS10 are tiny lights that run on an AA-sized battery. Larger lights are more powerful.

Hanklights (Emisar/Noctigon) also have the option to be configured many different ways. Hank is famous for shipping accordingly. Your choice of color temperature, some emitters available in actual (often monochromatic) colors like Deep Red, or maybe you want a UV light that has a filter that cuts the non-UV part of the beam out. Some lights, like the D2, offer multiple choices as they have two or three channels.

Metal construction doesn't mean much if you use cheap metal and/or bad machining. The build quality is notably better for enthusiast-grade lights.

In short, it's the difference between a decent restaurant and McDonalds.