You can change the natures, so don't worry about that.
Those Ivs limit your options, don't make it a sp attacker or a wall.
As @N1Dude said, Leafeon is the only one that can benefit from the high def/speed, just make sure not to switch it in a fast special attacker .
Btw leafeon learns swords dance by leveling up, so it's not that bad.
With a moveset with SD+leaf blade+knock off+ last resort/x-scissor/baton pass, it can make a dent in any team!