One point in your argument is different writing style, can you provide at least three scholars/historians that are not biased by being atheists? Another point you have provided is that it is written later than Paul's known epistles, can you provide evidence that this is the case by something more than assumption or presumption? The last point and a very important one, it was common during this time for appointed scribes to write for the Apostles but it was never common for scribes to claim to be the Apostle in the writings.
What does atheism have to do with critically analyzing writing styles? You're aware that there is a specfic, certain, literary methodology used by scholars and academics the world over to analyze ancient writing? Are you aware that these specific methods can be applied to any ancient text, by any academic or scholar? Are you aware that when these specific methods are used, they yield specific patterns of data, that when compared with known controls (i.e. Romans), they fail to reach the threshold that would put them without any doubt as having been written by Paul. Additionally, it was common practice to write letters and missives in the name of one who held sway or authority, so we know, and have other non-biblical examples of this.
Sentence structure, syntax, and words used of known writings can be compared to other writings, and using statistical analysis, writings can be categorized as either, a match, not a match, possibly a match, to the known author. Knowledge of subject matter is also evaluated; for example, if you have one work by a known author, and they exhibit a proficient knowledge of a certain geographical location, that when compared to an unknown work, the author is unaware of the previous authors knowledge, and this geographical information might be missing, or wrong altogether. Or, let's say a certain word wasn't used until a certain point in time, so anything written using these words, and claiming to be from an earlier time period, would raise a red flag.
So to answer your question, there are known, accepted, academic and scholarly approaches to critically evaluating ancient literature. These methods are available to anyone; atheists, theists, Baptists, Europeans, Americans, and even Republicans, and results will always be the same, regardless of who does the analysis. Unfortunately, what devotional historians tend to do, is cherry pick their data to support their religious beliefs. There are a few exceptions, I mentioned Metzger earlier, but by and large, they lose credibility when they're unwilling to take into account true academic methods.
As I've said before, I don't care what you believe, and I'm not trying to get you to forsake your religious beliefs, but at the least, you should attempt to understand the academic standards used to evaluate ancient literature, and why these conclusions are drawn. Again, it's incumbent upon you, to show why this methodology used for
all ancient literature should not apply to the bible.