I thought the deal with the expert sphere grid was that it had less nodes, but more empty ones that you could add things into yourself. So for example, adding attack+4 would allow you to max out attack faster than using the attack +1 nodes, or having to use a clear node to remove unnecessary spheres.

That and it lets you go basically wherever you want the characters to start on, rather than Auron Being a powerhouse, Lulu being a black Mage etc till they finish their routes