Review Detail of Gomuningen in Fairy Tail: Metal and Threads

Also instead of developing his magic he for some bs reason wastes his time building a car in a world of magic

He does improve his magic later in the story(Sun arc), or mb better to say that he already has the various new magics but is holding back? Dunno, author kinda implied that he had them for some time when he introduced them. As for cars, you need to remember how his magic works, he need to be familiar with various metals to analyze them to produce himself, so its kinda make sense for him to work and produce cars or Erza's armor.