It is true that a budget smartphone can do mostly what a much higher end device can do. No contest. The real question is that of how well it can do those things. I have the privilege of having owned and used well over a hundred mobile devices (and reviewed even more), if there is one thing I am sure of, it is that budget always comes at a cost. It does not matter what brand it is or how well hyped it is, if you want something affordable, you will have to make do with compromises.
For example, while the Motorola Moto G really is a good smartphone in many ways, the lack of expandable memory is a huge blow to many users. Consider that it has only a maximum internal storage of 16GB (there is also an 8GB version), and you can imagine how quickly a fairly heavy user can run out of space. After that, using the phone becomes a frustrating experience.
A friend who owns a Moto G tells me that he now has no choice but to switch to another phone. He has filled up the Moto G’s internal storage twice now. The last time, he had to offload some files to PC. How many times should a heavy user have to do that? He is a heavy user. The Moto G’s compromise is cramping his style. 32 or 64 GB of internal storage would have been a better idea. But budget.
Sometimes, it is the build quality that suffers. Sometimes, it is the display. At other times, it is battery capacity. Perhaps RAM. Maybe storage. Camera too. Many times, a combination of things. However you look at it, budget has a cost. Any time you find that you can afford a slightly more capable device, trust me: spend that little extra and thank me with a pizza later.