The damage-vs-drain/penalty point is key.
Damage continues to build. In theory you could do hundreds of points of "damage" to an attribute, just like you can do more and more damage to HP. Penalties do not build - only the largest value from a given source is valid. If you hit it 3 x with ray of enfeeblement, it's penalty is whatever your "biggest" ray of enfeeblement happens to be.
Helpless isn't auto crit like it used to be, but it's still very useful. There are plenty of times on my Pale Master I wish I had just one more source for a penalty in order to make some red/orange more manageable ... so much so that I'm considering a LR/TR to fit in the proficiency (and maybe even precision, no lie). As it is, I carry a +5 STR sapping stick of some sort and a STR-sapping returner.
....
I would totally love to see more named d-axes though.