He has the following to make up for it:

- Bull rush every 30 seconds, with 75% damage reduction during
- Passive skill 'heavyweight', if he drops from a height near other champions he does damage to them
- More max health and armor
- Spawns with 50 armor
- More resistant to weapon knockback (not 100% confirmed but seems likely from watching the videos)

Would you want a champion with that kind of killing power and tankiness to also be able to move as fast as other champions? I don't think so.

He can still rocket jump too.