Generics are so subjective that brand loyalty to manufacturers plays a very big deal, in my experience. There are only a couple of generics that are a bit shoddy, like Mylan Diazepam and Mallincrodkt hydrocodone, but all this bagging on TEVA is strange. The Adderall 30mg IR and Dexedrine 10mg IR/ER produced by TEVA (owns Barr) seems potent enough to me, although I've only compared it to CorePharma 20mg IR Adderall.
TEVA has shoddy manufacturing standards, but they're not going to skimp people on active drugs that won't even save a few pennies per tablet on their end.