yeah, it depends on personal tastes really. In our group, we love that there are pcs of different levels, it feels very old school and sort of videogame-y (in a positive way). But we also love very unbalanced parties in general (like, gandalf-aragorn-frodo, or superman-batman-robin), it makes the story more like actual movies and books, and last but not least, characters interaction and bonds are wonderfully fueled by differences like these. In DW, a character with a lot more levels than the others not only is usually the more active one (because he rolled more, resolved more bonds, and always followed his alignment), but is also the character who has seen the worst things coming by, and that counts for something story-wise!
Also, XPs on a miss prevents the "avoid the system" approach, where the players try anything to avoid moves where they have +0 or -1.
- "I do it!"
- "it's a move! Roll+0!"
- "wait wait, you're right, better try something else then"
But obviously, I can totally understand when a player sees himself two levels behind the others and feels like it's "unfair".