Now, Stevie did have two guitarists in his '70s touring bands, one of whom was Michael Sembello, who later had a hit with "Maniac" from the Flashdance soundtrack.
Your post prompted me to read up on Stevie's early-70s period and the musicians who worked on those albums.
In a 2021 interview, Sembello shares a story about when Wonder first hired him on. Keep in mind that Sembello was still in high school at the time:
I just happened to be in the right place at the time thanks to a friend of mine. He woke me up one Sunday morning and told me that this guy named Stevie Wonder was looking for a musician. Back in the late 1960s and early 1970s, I really didn’t know who he was, but I heard about him. I was into John Coltrane and a bunch of jazz stuff back then. I asked my friend, “Is it that blind guy?” He replied, “Yes, that is him.” My friend told me to come with him because he really wanted the gig. So, I went there with no knowledge of who Stevie Wonder was or his music. Fortunately, for me, this was when Stevie started to move into his jazz phase. When I showed up to the tryouts, there were a couple of hundred different musicians waiting in line. They all had Stevie Wonder’s music and his books with them while they were sitting down. It was kind of like a game show.
I remember one of the guys saying, “What song are we going to play Steve?” Everyone started flipping through their Stevie Wonder song books. Stevie replied, “Man, just follow me.” And that was the beginning of him playing Coltrane stuff. I started to play and by the end of the audition, I was in pretty strong standing and quite perplexed because I really didn’t know what I was getting myself into. At the end of the 1960s, there was still this whole segregation thing between the whites and Blacks. Most Motown bands didn’t have more than one white player in their band. [Stevie] already had a white trumpet player and there was an argument going on in the corner of the studio. Ira Tucker, who was the publicist, told Stevie, “Look, you don’t realize you hired a White guy.” So, Stevie motioned me to come over to him, and he said, “Hey, man. What’s your sign?” I didn’t know what he meant, so I thought he was asking me what my nationality was so I answered him, “I’m Italian.” Stevie turned around and said, “Guys, he’s Italian. He’s not white. He’s in the band.” [laughs]