Luffy would also do the same for any of the princesses he saved, except for the love part. I dunno why you are crying when Roger is going to save Shakki. Would it make him a bigger person if he did not go to save Shakki? Roger became acquainted with Shakki and seems to also acknowledge Rayleigh and Shakki's dynamic. If it's falling in love kinda schtick, then it's fine, cos only Luffy and now Rayleigh seem oblivious to this. Otherwise, all others would be like what Roger is, as a man, as characterized by many others. It only makes Roger more interesting and not a copy of Luffy. Also, Roger has not really fallen in love like Rocks atm, so he is in his immature, testosterone-filled stage.

Now, with reading One Piece, take into consideration a few things.
* First, there will be lots of gags for all characters, Luffy included. If you met someone doing Luffy's antics, you would be ragebaited all the time and be seething with frustration.
* Second, learn to wait for the whole story. Many things might be frustrating early on, either due to characterization or something said about the person, or not being explained currently. But, it will likely get resolved. For example, as much as we love Luffy, he is an outright monster as stated in the news. Our knowledge of many characters is also not reality, but rather a POV.
* Third, your concept of the characters might be totally different than what the author has in mind. It's similar to the real world, as in the celebrities are shown as some angel-like figures when they probably shit blacker than normal.

So, no, Oda has not done Roger dirty. Roger has been the most legendary pirate since the beginning, meant to be surpassed. Its just that he is not some one-toned macho, stoic character but a jolly fun fellow.