Ah. Apparently, Nicky has clarified this: Tigress’s stats aren’t actually at +150; they’re between 120 and 130, but for one reason or another she can trigger stat checks of 150+.
As for 150, he clarified that this value is actually the absolute base stat limit, in the sense that you can temporarily exceed it through spells, transformations, gear, etc., but the base only goes up to 150, even for the geniuses of the Celestial Realm. With the exception that only PER and CHARM can exceed this limit at the base level. Now, it remains to be seen whether this will remain the case, or whether this even applies to Ruo.