Referring to Protestantism as a single religion is questionable. The denominations within it don't agree on what salvation is, how to get it, what happens after, what the proofs are thereof, or even what and where and when heaven is. Even something so basic as who Christ died for is up for debate (did He die for all, for some, for those God foreknew, for those God forced to be saved?). The one thing that seems to hold it all together is anti-Catholicism. On that pretty much everyone can agree (except the Anglicans, they seem kind of OK with Rome).
What you seem to be targeting is the Evangelical Protestantism. And the rebuttal to saving faith (ie: belief) is quite simple: James 2:14-26, particularly verse 19: "You believe that God is one. You do well; the demons also believe, and shudder." I'm sure many other verses could be produced to describe various things that save us besides faith, but this one has always been a powerful challenge to the "all you have to do is believe" argument (not to mention that logically, this is still a work of the individual, hence Calvin's irresistible grace).
For whatever it's worth, it's the negatives of Protestantism that drove me away from it, seeking something healing and edifying, and the positives of Orthodoxy that answered the search. Still trying to figure out how I fit into that picture, though. All that said, I have met spiritual mature people with pure motivations and servant spirits, so I cannot with one fell swoop condemn all the fruits of Protestantism as rotten. Sola Scriptura and prayer can get you a certain ways, I believe, legitimately. It is when one runs into specific questions of doctrine or practice not addressed in Scripture that it all breaks down. And then it can become a catastrophic failure.
But these are just my thoughts from my limited observations and experiences. Take them for what you will.