If you want a tame giga that almost as strong as wild giga then just breed 2 high lv giga then fully imprint the baby

Sure it will take hours of gaming so be sure to imprint the baby then wait for it next care, while you are waiting you can do other thing like do your homeworks or housework or simply play other game to make good use of your time,just be sure that you check the baby giga often so it wont starve to death