For a series that has never passed the 800k threshold it sales are fine for a platform of which no fan base was cultivated on. Selling less than on platforms with more cultivated fanbases does not make it the biggest bomb.
Just look at the sales of the original mothership titles :
[PS2] Tales of Destiny 2 - 762,861
[PS2] Tales of Symphonia - 390,414
[GCN] Tales of Symphonia - 311,473
[PS2] Tales of Rebirth - 596,493
[PS2] Tales of the Abyss - 556,465
[X360] Tales of Vesperia - 204,305
[Wii] Tales of Graces - 212,769
[PS3] Tales of Xillia - 632,151
It's obvious that when they decide not to release games on Sony platform the sales just weren't there, for Vesperia they had the M$ money and worldwide sales to help but even with that it just wasn't enough for them and that's why we'll probably never see a Tales on a Microsoft hardware again.
As for Graces what did Nintendo bring them ?
Nothing, no money no localization help, no sales, and the incapacity of patching their own game (something the Team Destiny's games are used to, the one before Graces, Destiny Remake, being delayed two weeks before release because of a similar problem)
But maybe it's a mere coincidence if weeks after the release of Graces the Tales Studio was on the verge of dying