They changed the terms of everyone's contract.
They can not force you to accept them nor can they enforce an ETF if you choose to leave Sprint because of these changes.
Changing contract terms without proper notice is a no-no.
I mentioned this to the rep when I called to complain about the issues with the Optimus update and was told that I cannot break my contract without paying the ETF.
You will need to escalate your case.
A customer Service Rep doesn't have the authority and is following a script.
You may have to actually have an attorney send a letter to Sprint informing them of their obligation and the legal precidents.
The fact is Sprint can not change user contracts without users agreeing to those changes.
You don't need to hire an attorney. Just go to your local small claims court and file suit against Sprint for breaking its contract with you. It costs about $25 or $50. After Sprint gets a couple of thousand of these suits, they will start dropping the ETF for Optimus owners.