I disagree about power-leveling. The solo/exp. egg set up against the Tumbleweeds nets you a good chunk of XP, but even better, they go down faster than the Tyrannosaur. Why waste time casting Ultima and using Genji Glove/Offering combo against Tyrannosaurs which will take a few minutes to do so when a simply Level 3 spell/ Tool/Dance/Blitz/Fire Skean/ Swordtech can decimate the group in a single round and have you finishing another round by the time you would have beaten a group of Tyrannosaurs? In an hour, I've been able to make the whole party jump by at least 10 levels with this strategy, whereas fighting Tyrannosaurs is a team effort and trying to solo them is more work than its worth, not to mention you don't have to worry about accidentally running into a Brachiosaur and watching him Ultima your party in a single round. Let's not forget that Tyrannosuar's utilize heavy damage attacks like Bite, and only appear in groups of two as a Pincer Attack meaning they get offensive advantage, meaning Bite has a much greater chance to K.O. a party member. It just requires more work than its worth.

The Tumbleweeds, are safer and far less time consuming. Yes, the Brachiasaur drops and carries good loot, but if the goals are levels, its better to not tangle with the one thing in the game who actually can one-shot even a high level party, especially since level grinding tends to make players sloppy and forget to save.

Besides 2 Tyrannosaurs net 17,600 XP which nets each party member 4,400xp or 8,800xp with Exp.Egg

4 Tumbleweeds nets you 10,216XP which is translated to 20,432XP for a single character in the solo/Vanish/Exp. Egg set-up.

Considering you need between 30,000 - 50,000 XP per level, to gain a level after Level 60, you're looking at gaining a level almost every two fights, and a guaranteed level for a character before getting to level 60. As oppose to a T-Rex team where even having everyone equipped with Exp.Eggs means they will still have to fight 3 or 4 battles to get a level. The only time consuming part with Tumbleweeds is that you need to do it individually, but Tumbleweeds have literally half the health of the Tyrannosaur and are weak to fire elemental meaning even low level characters can wipe them quickly in a single turn, even faster if the controller is set to memory. If the player only wants to beat the game, getting to the 40-50ish range is a breeze, and would probably take an hour at most.