Which characters would you say are better?
At the point you're at, it's a toss up. Like I said, Melia at that point just has cooldowns that are too long for her to really function as well as she can. After a couple more areas she'll probably be the best character in the game for quite a while, if you use her.
But once you hit level 90+ or so (or start tackling those sort of enemies/challenges) Shulk is the best character in the game, unquestionably. Nobody can touch Shulk's combination of utility/support arts plus very good DPS without relying on damage over time (DoT).
After that it's debatable. I think Dunban would easily hold the #2 spot, because he's probably the second best non-DoT damage dealer and his role as a speed/dodge tank is much more useful than Reyn's damage eating. He can tank anything in the game, even if he's lower level than it is. In my late/post-game low-level run, he tanked a level 79 enemy at level 71 without going down with only minimal healing (Light Heal only, no Sharla) without any sort of special setup, and didn't have any problem against the highest level superboss at only level 79 (I have a video, but don't refer to it yet since it contains spoilers you're not at yet) - granted I did have a lot of post-game stuff you normally wouldn't have at level 79, but still.
Melia and the 7th character are probably tied for the #3 (7th character also drops a slot this late in the game, earlier that character is probably #2 behind Melia). Melia is really only good at dealing damage, her support arts aside from Reflection are just not that great. Sleep is only useful if you don't have Shulk in the party. She's too fragile to tank.
7th and Melia are probably tied for the top damage dealing spot, Melia might have a slight edge due to DoT (is slightly lower without DoT probably), assuming each are properly setup. 7th has a little more utility and is very self-sufficient, I was screwing around and solo'd enemies 6 levels higher than I was with that character. I don't think any other character in the game can do that reliably. And with the better setup that I have now, I could probably do enemies closer to 8 levels higher.
But this is all kind of pointless, because you can use any party and 100% the game. Some setups are more effective than others, but it ultimately doesn't matter unless you're dealing with self-imposed challenges.