Tyrantitar is still going to be a beast in this generation, despite all the weaknesses and new fairy type threats. The assault vest gave it more options and less predictability to go with it.
I see it as an effective check or counter to MegaGengar where he can potentially KO with pursuit, crunch, or EQ since it lost its levitate. According to calculations, with careful nature, sandstream, and assault vest, it can reach up to 738 sp. def. So yeah, it's more specially tanky than Blissey. From other sources, it's able to survive a focus blast or two from MegaGengar, as well as about 5-6 hydro pumps from Rotom Wash which makes it a bit ridiculous. Though with that setup, it leaves it a bit weak on the physical defense side, where bullet punch from Scizor can give it trouble.
Anyway, at the very least, without frisk, you'd think it could be running a choice band/scarf set. MegaTTar is also something else as dragon dance is an option for it once again in this generation, but it'll at least tell you what item it has.