I get the logic, I'm saying its inconsistent.
Junglers clear each camp with different speeds and at different health. Ivern is an anomaly - he clears each camp at the same speed and the same health. We assume he is balanced around this: if he goes for a full clear, he isnt clearing exceptionally fast, slow, high health, or low health. Maybe he clears a little faster due to his efficiency, but thats his niche.
Single target junglers can clear buffs/gromp faster than AoE junglers. AoE junglers can clear Raptors or Wolves faster than single-target junglers. But you dont see XP being hindered for Single-Target junglers on Buffs or AoE Junglers on Wolves. Ivern, as a unique jungler, can clear Krugs faster than any other jungler. Though it might make sense to hinder his clear due to this unique trait, its not something thats consistent with XP gain in the jungle.