I wrote down a list of offensive spells for each dragon quest hero from the main series. It might be useful to see side by side. I think that considering smash, it might not matter since characters can share some things, but here it is:
1: [Non-elenental]
2: [No Magic]
3 (Erdrick): Lightning, Fire, Explosion
4 (Solo/Sophia): Lightning, Fire, Explosion
5 (Madason): Wind
6 (Rek): Lightning + All spells from other classes
7 (Auster?): Lightning, Fire, Explosion, Wind + All spells from other classes
8 (Eight): Lightning, Fire
9 (Nine): Wind, Ice + All spells from other classes
10 (Anlucia).: Lightning + ?
11(Luminary): Fire, Explosion, Lightning
I know for sure that Anlucia can use lightning magic, but I'm not sure about the rest because there are no english site for it and I had to look at google translated names.
We can see that Erdrick, Solo/Sophia and Luminary can all use the exact same elements. And actually so can Auster's hero class (So 3, 4, 7, & 11). Rek only has lightning but can use other magic classes too. The only heroes that can use wind are from DQ5, 7, & 9, (+ 6 if we count other classs). Only 9 can use ice magic normally, but there's technicall no hero class (Minstrel). Eight doesn't have explosion, but at least has fire ;p
Maybe that can give some ideas, including for the dream idea of an echo character with something different.
There's lots of weapon skills and other spells too.