Well, dunno if my opinion is particularly wanted since it might make the situation more complex than it is, but I might as well put my two cents in as someone who's read both the manga and watched the anime.

Don't see a problem with the rest of the CS, 'cept for the Flames stuff.

Reborn mentioned that other Families have begun to develop bootleg DW Bullets, and that was only a week after the Future Arc. This is 20 years. That, plus the 7 year training bit, is enough justification I'd think. Now if she were getting Dying Will Mode [i]without[/i] Bullets/Pills, then I'd have a problem. Though I [i]do[/i] dislike having two more custom Flame types with no justification apart from having a special weapon with special properties. Especially since before Decimo, only the Vongola had the capacity to use Flames (not counting Flames of Wrath or Mist Flames, which apparently anyone can use without having a ring or special weapon). Though if it had just been considered a fancy-ass katana before Flames came along and they discovered it's capabilities, [i]then[/i] I might budge a little.

Also, Sun Flames don't sharpen, Lightning does.

...Might give my opinion on whether it's OP or not, but after I go for dinner.