Yeah. Although, in the HD versions, there is a sphere grid call the expert grid. Basically, it allows you the freedom to teach and follow whatever paths you want. So, if you wanted Yuna to learn Lulu's black mage spells, she could much easily than with the standard sphere grid.
However, it's not as easy as it looks. XD I've tried it, and I found it hard to figure out the paths I wanted everyone to take. Also, I know Rikku isn't much for battling, but I still adore her because she's honestly my most favorite character ever!