That would only be true if 5e followed the same character creation rules as 4e that include the "any one skill" exploit. That is more a problem with the current character creation rules and School design rather than an actual problem with the suggestion.It occurs to me that, if you take the various benefits currently from Mastery abilities and move them into Kata, you could then give a completely consistent set of Mastery abilities to the Weapon Macro skill.
That said, I think that 1 kata per level is a bit much: some schools would get 3 kata at character creation before spend the starting XP.
I actually like this idea. It always felt ironic that bushi often gained more combat potential from improving their courtly abilities than they did from improving their combat abilities.Can I suggest that Kata actually give enlightenment? It would be a way for increasing insight besides skill spam.
As you say, it doesn't make sense. Make kata grant insight equal to the XP cost -1, or /2 or something,