Don't be afraid to make them OP, just make sure everyone has OP class mastery. If it's just mostly stats than there is no way it will make subclassing not viable whatsoever, it will still be mandatory for all kinds of supports(pvp/pve), but even if it will be overall less viable than subclassing... Is it really bad? Shouldn't have subcalssing been an option? Because at this point it's cleary not, gap between subclassing and pure classing is ridiculously high(exluding new DK, but even there subclassing is still overall better).
Was subclassing intended to completely destroy class and build variety and identity? Of course it wasn't, but it did. And now you have a chance to fix this to some degree, but 7% crit damage passives are nowhere near enough for that, please make them stronger and don't be afraid to make them too stroong as long as they are too strong for every class.
I understand that they are meant to "stop gap measure between class reworks", but there is soo much time to wait for these reworks, we have to wait for almost 2 years to get all of them, and if these passives are released on current state it will not change anything at all, pure classing will still be underperforming and in no way competitive compared to subclassing.