That’s what indigenous languages tend to be like in one way or another. Languages “grow” in complexity the way that people pick up habits and cars pick up rust. One minute the way you mark a verb in the future tense is to use will: I will buy it. The next minute, an idiom kicks in where people say I am going to buy it, because if you are going with the purpose of doing something, it follows that you will. Pretty soon that gels into a new way of putting a verb in the future tense with what a Martian would hear as a new “word,” gonna.
In any language that kind of thing is happening all the time in countless ways, far past what is necessary even for nuanced communication. A distinction between he and she is a frill that most languages do without, and English would be fine without gonna alongside will, irregular verbs and much else.
These features, like he versus she, certainly don’t hurt anything. A language isn’t something that can be trimmed like a bush, and children have no trouble picking up even the weirdest of linguistic frills. A “click” language of southern Africa typically has not just two or three but as many as dozens of different clicks to master (native speakers have a bump on their larynx from producing them 24/7). For English speakers, it seems hard enough that Mandarin Chinese requires you to distinguish four tones to get meaning across, but in the Hmong languages of Southeast Asia, any syllable means different things according to as many as eight tones.
What the World Will Speak in 2115 By JOHN H. MCWHORTER
Language of the Future