Hiragana, katakana and kanji are all used in written Japanese.
hiragana is needed for grammar and vocabulary, as well as reading furigana, whereas katakana is just used for specific vocabulary (and 30% is a high estimate) like foreign names and loan-words. Hiragana is more vital to learning grammar than katakana, so I don't know why anyone would start with katakana. To beginners, katakana is pretty much only useful for writing your own name or simple vocabulary like パン、ベッド、チーズ etc.
The reason people have a hard time reading katakana is not because they focused on hiragana first, but because they didn't focus on katakana enough. It comes with practice.