So what is too much cam lean (limb twisting)? In my opinion there should be none whatsoever, but this won't happen so long as the cables are pulled to the side by a cable rod/slide or roller guard. This is the technology we have been stuck with for the last 35 years. It's always been in the design, but as bows become shorter the angle of side pull becomes more acute so more noticeable.
So why isn't something being done about it? IMO, simply because we, as consumers, don't demand it. Limb failure rates are acceptable enough that companies can just replace limbs. Limb failure borders on about 1% across the industry for all reasons. And as much as that may be acceptable to most it's not always so for the person that experiences it. So long as we keep buying bows with this old technology they have no reason to address the issue. We, as consumers, are more interested in how much shorter and faster bows can become; not how much more reliable easier to tune, and pleasant to shoot.