Seven Year Tribulation: Protestant Purgatory?

I think that the 7 year tribulation period posited by many Pre-millennial protestats is the equivalent of what I will call "Protestant Purgatory". Here we have a scenario where we have believers who are rescued from the Tribulation by virture of the fact that they have simply believed in Jesus and received God's grace. But those believers that come to believe during the Trib. are NOT rescued during the Trib. And why not? Well, for no other reason than timing. Their timing was off and so they are punished or 'purified' through an intense trial/tribulation, EVEN THOUGH THEY BELIEVE, while others are afforded divine protection and escape BECAUSE THEY BELIEVE. Isn't this strikingly similiar to a concept of Purgatory? We have some believers who are given preferential treatment due to their belief while others are not, even though their belief is the same. The reason for the difference is that some acted faster than others. I hate to use a cliche, but it's really a judgment based on actions/works and not a judgment rendered due solely to anyone's faith. The judgment rendered is not actually based on their belief (since fairness would say they get the same verdict), but rather it's based on their timing. I think it's a form of Purgatory as Trib-believers are purified for flaws in their faith (lack of promptness), while those of us without that flaw get to skip the intense purifying. And this is only one problem I see with it.