I think rewards system should be fixed as well, a box could be obtained in nightmare mode, maybe? then rare dogiball should be on very hard mode, since it's hard to obtain it.
You know what would be better? Getting better rewards from world bosses. Instead of a title, how about getting a title from other dungeons like if you completed it and it gives you like 10 dex effect of the title for completing the dungeon, I know there's a title for cc150 if you complete it. How's that for TMQ4 hard mode and upper ones? I'd say for the titles can be obtained in UD6 since it's very long, right? We could do that for the VERY last boss.