[dappa]

yes your right, new characters who join your party have the same level as Zidane when they join your party.

But what happens is they join with lower stats and ability stones for unknown reasons. If for example you powerlevelled zidane up to level 99 right at the start of the game everyone else would be 99 when they joined but would have stats that were around 10 to 20 less than they would if you had played the game normally. You can get round this by leaving zidane at low levels until you have all your characters in the game join you then power levell your characters to get their true stats