i always assumed that the little triangle next to a companions percentage meant they wouldn't jpin in battle so i never trained them. now they join me and tey're like level thirty while i'm level 43
That little triangle means that they have less than one percent of joining your combats. This does not mean that they won't join, it just means that them joining will be very rare. Make sure you keep up with their training. It's important, even if they won't join battles very often.