No one was bullying her until after Leonhardt mentioned it.
Gods that hurt to read; but don't take your own lazy reading and blame it as "lazy writing."
Page 17 lays out all you need to understand -- Celia is special in her ability to form multiple contracts, so won't face a similar restriction to one attribute like Leonhardt now has.
Nah I actually agree with the first poster. The chapter specifically says Leon lost two magics due to contracting with Ifrit, my best guess since its a great spirit. But there is actually no connection between contracts and magical abilities mentioned in this chapter. So definitely seems like an ass-pull by the author to make MC hated by nerfing him, which is further compounded by ass-pull, in making the number of magic types, rather than the proficiency of the magic use, which is literally the standard in most other magic related works, to be judgement of quality.
Its effectively the same nonsense as these works were gravity, healing, support, etc is looked down for no reason other than the fact that's the only way the author can make a clearly useful or base breaking ability seem mundane. Like if the guy can use fire to the point he can raze a nation to the ground, its kind of arbitrary to say someone who can use magic earth and water, but only to make a mound and luke warm tap water, is stronger.