I think I selected "Expert", what's the difference?
And I just want to finish the game really and experience a few cool easter eggs.
After looking at the Sphere Grid, I noticed Tidus will need to get roughly another 20 sphere levels before he comes across another "Strength" sphere, they seem to be so rare.
Normal Shpere Grid has more defined roles and in normal game, you have little chances to go wrong way. In Expert Grid , you are more free, but if you don't know where to go, you could end up in problems. Well, this problem can by "solved" by some Sphere Levels, but it take time. Oh, and Normal Grid has more nodes (860 in Normal, 792 in Expert), but if you don't want to maximize stats, it doesn't matter one bit.
Tidus overall isn't character with much strenght, it's Auron or Wakka role. He is more for speed and cast Haste/Hastega.
Xen: 30k HP and 200 in stats isn't exactly much for Penance and harder Dark Aeons.