Hey Pak and welcome to URC. Sorry to hear about your bad experiences. I have had three of these little Tetons and found them quite durable, going for months between repairs - but our styles of driving may vary. I started exactly one year ago with a Teton for my 8yo and it just snowballed.
The body mounts does break, happened to two of mine but in a way, that's better than breaking the body. Diffs are weak, but reasonably straightforward to replace as they wear out. I did the Team Associated diff mod and lent that car to a friend but he still has not driven it yet.
Upgrading the Teton to take more abuse is costly, there's parts but they do add up a lot of $ and everything stock is basically "just enough" - you will just move to the next weak link in the chain. That is sort of the case with all RC cars though. Cyrano, the guy who started the "Bible" thread is a major fan of the Teton platform and that's why he did it all.
I like it too but I liked the 1/16 Traxxas much more and decided to move on. They are, IMHO, tougher. Maybe moving soon again - currently rebuilding a 1/10 Stampede and getting to know it.
Anyway: Dont give up. It sucks that you got off to a bad start and obviously you need a more durable car for your kid. Use the opportunity and get something else - if money allows it. It's not an entire waste of money because you got started and learned something and the Teton will sell on eBay.
So far, I've managed to break all but one of my eleven RC cars at least once and judging by the forum members things break. Many members have experienced the "it breaks every time I drive it" blues. Without statistics it's hard to know which cars really hold up to abuse but some models stand out. My Traxxas 1/16 cars do NOT I have had all the standard "breaks" and I think they would be too weak for your purpose but they are good enough for my kids.
Maybe a 4x4 Slash will be tough enough, but I have almost no firsthand experience with it. Arrma seems very strong. They are usually a bit cheaper to buy.
Edgery on Soundcloud - New album Aug 22 "Endless Summer"
LaTrax Teton, 2x Traxxas 1/16 MERV, 1/16 Slash SC, 1/16 Summit VXL, p4de VXL