Well, what is optimal? The first time I played Fallout 1 it was optimal to me to have a high barter skill, because I traded a lot and want to not lose money on that transaction. Later I found I can steal money, so I focused on theft skills instead. Years later I didn't play all too morally any more, therefore I could kill whole cities which meant weapon skills were more important than barter or theft. A few months back I played it again, and this time I found shooting people is boring, because I did that in all my playthroughs before. So I began using only melee weapons/skills on my character.
Optimal is different for different players and will change over time. A good RPG has a very high number of optimal or only slightly suboptimal paths you can choose from. I would even argue that sometimes the suboptimal paths are the more interesting ones (real roleplayers play their character in way that they might be scared of rats and run away, even if their character is able to one-shot the end boss; another example is above me deciding to only use melee weapons and make the most of it).
For any goal, there's only gone to be one (or a best a couple) optimal builds. Among players, the vast majority are going to have one or the same few goals.
In a MMO, most players are going to be chasing the most overpowered build. Which is why MMO developers change things all the time - not for supposed "balance", just to keep players on the treadmill.
I agree on the MMO part. That's why for me MMOs aren't really RPGs. My statement about good RPGs was a little different, though. A good RPG really has different optimal builds, e.g., you can't say that one of the starting characters in Diablo 2 is really better than the others. If one build overpowers the others that's really a balancing issue and a game claiming to be a good RPG has to make sure that this doesn't exist. As you say I also believe that MMOs have the goal to keep players on the treadmill and therefore prefer a changing imbalance over a constant balance.
Optimal is different for different players and will change over time. A good RPG has a very high number of optimal or only slightly suboptimal paths you can choose from. I would even argue that sometimes the suboptimal paths are the more interesting ones (real roleplayers play their character in way that they might be scared of rats and run away, even if their character is able to one-shot the end boss; another example is above me deciding to only use melee weapons and make the most of it).