You are right. Or I hope you are, so that I can feel better about not wasting my money and time. hahahaha!
Seriously speaking, since most introductory books are written for 4 string bass, I just ended up learning the basics. After the first 4-5 books, I started to work on walking bass lines and that was when things started getting confusing but at the same time as I started working on approach methods, I realized the true power of a 5 and 6 string.
I don't have long fingers or long arms. And to my surprise, 6 string was easier to use since stretching arm and fingers wasn't necessary. It did take me time to figure out the notes though. But once I got a hang of it, more strings the better.
In all honesty, a 7 string fretboard is really wide. You can't do slap so easily or machine gun thump and pluck the octaves that easily. It puts a lot of strain on the wrist, especially if you have to work on the same passage over and over again. This alone is novice unfriendly and will cause tendonitis, so being realistic 4, 5 or really narrow spacing 6 string was/is a good choice.
The string to string spacing on my Yamaha TRB6P is wider than the standard P Bass. Plenty of room for slap, thumb, and double thumb if that is your cup of tea. IMHO, the most challenging aspect of slap on an extended range instrument is muting.
I do find fast patterns that jump random octaves and fifths to be a bit more difficult with my TRB6P. Partly because the spacing is so wide and partly because the extra strings increase the level of uncertainty. This type of pattern is the only area where I have found a 4-string slightly superior.
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