There are ten types of latent Tamadra that, as far as I know, will be in this dungeon. The dungeon costs 99 stamina. So assuming a 100% droprate, which I'm not, that gives you a 10% chance on each run of getting the one you want. If you're spending stones to farm, that's going to cost a ton of stones.
Meanwhile latent invades allegedly have a 10% appearance rate (although my own numbers have been very consistent with 5%) but with a 100% chance of getting the one you want, and for half the stamina.
So if you want a ton of the same latent, it looks like doing it the old way might still be good, since it's not on a timer. But farming in the new dungeon meams you'll be gaining a ton of MP in the process, and possibly many more Tamas overall even if they're not the exact one you want. But again that relies on a 100% droprate that might not be there.