Till chapter 700, roland stay the same... well he is not that weak u know.. he got guns and a lot of witchs waifu...
*Possible Spoiler I do think he will gain power. You know the witch with the power of "Battlefield of the Souls". It was a witch of the church. The winner of that battle will gain everything from memory to magic power. I hypothesize that one way or another, she will challenge Roland using her powers and she loses. So Roland gains everything including magic power and thus become the first male witch. Hehehe, just my own theory.
Spoiler Well, you're right for the most part except he didn't gain everything, he had to work a little bit more to obtain information in soul Battlefield. He can't use any magic after he defeated Zero, but he could use Zero's ability when he's sleeping
Chapter 230-231 reveals that there are wizards which seem to be male witches just that they are even rarer.