Life is built on contradictions. There is only one thing that balances all of those contradictions...
The Rule of Cool (or the Rule of Fun/Money)
If people are having fun, then its good.
If SSG makes money, then its good.
This is the basic transaction, the holy grail of trade, consumption, and creation.
People are opposed to power creep because its not fun. It ruins challenge.
People are in favor of alts because
experiencing the diversity the game has to offer in terms of builds... ...is fun.
Do you REALLY THINK THAT ALTS MAKE THE GAME THAT LESS CHALLENGING?
And then you can balance Character diversity (and enjoyment of that) with an increasing level of "player power."
You should also keep in mind...
...power creep and mob power is arbitrary. Those thing can ALWAYS BE CHANGED.
Goldilocks is looking for porridge that is just right.
No one cares about power creep IN A VACUUM, but instead IN THE CONTEXT OF COOOOOOOOOOOOOOOOOOOOOOOOOOOOOOL.