I don't know what percentage of languages use gender for nouns, but the language I know second-best (after English and before Spanish) uses gender, too (German).
I find using gender makes things more complicated, but also more clear/precise. zB, when you say "the teacher" in English, it doesn't tell you whether the teacher is male or female (without adding "lady," "female," "male," or "man" or some such additional word).
In German, it's clear: "Der Lehrer" is a man; "Die Lehrerin" is a woman. Spanish similarly ("El Maestro/La Maestra" and "El Profesor/La Profesora").
So: more difficult? Yes. Superfluous? No.
And speaking of difficulty, I have heard many people over the years say that Spanish is an easy language to learn. Maybe I'm mis-remembering -- or maybe it's that my brain just isn't as agile as it used to be -- but it seems to me that learning Spanish is considerably more difficult than learning German (which I did half my life ago, when I was in my mid-late 20s).
Maybe part of it is because English is a Germanic language?
I hope this doesn't sound politically incorrect, but I wonder if people say Spanish is "easy" in the same way that they say learning to play the guitar is easy: while it's true that it is relatively easy to learn a few chords and play some basic rhythm guitar, to really know how to play the guitar well is extremely difficult. And I'm under the same impression (delusion) about learning Spanish well - it's pretty easy to learn a few conversational Spanish phrases, but once you get beyond the "holas" and "adioses" is where "there be dragons."
Maybe it's considered easy because many Spanish speakers (perhaps not those from Spain, but the Latin Americans) don't seem to be ones to read very much or widely (and/or may tend to be under-educated) and hence their vocabulary isn't that great.
IOW: learning a little guitar and a little Spanish isn't that tough; but to really know them is another matter altogether.
I also find Spanish -- although consistent in its orthography and pronunciation, as German is (and English is not) -- very hard to pronounce correctly - it's as if I have to adjust the way my mouth "sets up" to speak Spanish, whereas German (except for the rolling R) came pretty naturally to me.