Several people have gotten through tough spots by lowering the game difficulty to easy, so raising it to medium would make that fight more challenging. However, now that you have a technique down that works for you, you would probably be able re-do the fight on medium, if you wanted to. Even with a save before the hall of echoes, you might be able to visit a few merchants and upgrade enough equipment to make a noticeable difference (if you hadn't checked them that level, you could save first, and then keep loading until they offered something useful), or re-skill in the battle tower.
If you get to the end it counts. Beating the game on easy may not be as 'good' as medium or hard, but its not like anyone is keeping track. Nobody gets everything perfect in one playthrough, anyway (unless maybe they are closely following a walkthrough/guide, which kind of defeats the purpose of playing IMNSHO), so if dropping the difficulty bothers you personally, then make another character and play again, using what you know to make a better character build and get all the quests, etc. If it doesn't bother you, it is pretty safe to just assume you could do significantly better with a second character.
yes its tough sometimes but the more the satisfaction you get after defeating it