Juggernaut's practically useless compared to Magus and Devourer, which is a shame because the last incarnation of Golem was actually really good. Taking off the gold gen passive was enormous to all junglers. Now you really do have to either farm or gank, and ganking is almost always preferred because of how brutal the monsters are. You CAN clear, no one disputes that, but pick Naut into Lee and you'll be begging for the old jungle back. That's fucking retarded. How is that possibly constructive? Oh, they're not ganking as early. Yeah, that's cool for the laners, but it gets fucking old after WW/Lee/Udyr kills me again and again in my own jungle despite my level, gold, health, and buff advantage.
How to fix: Update tanks. Mana costs have been meaningless gates almost exclusively meant for tanks for too long. In a game where Yasuo and Lee exist, you can't gate a champ with mana with a straight face. Cooldowns too. Look at Hecarim's W and E cooldowns and tell me that's okay.
Reintroduce the old Golem. The quill passive, the gold generation, the bonus health, etc.
Make some buffs give defensive assets. I don't even know why that isn't a thing.
For Naut specifically, make his W on hit persist as single target passively and leave the splash on activation. Make his passive on hit magic instead of physical. Lower the cooldown and mana cost of his Q so he can actually utilize the terrain hook. Up his base MS because Lee Sin exists with 350 MS despite HIS Q and W mobility. Update his model size to reflect the fact that he's a huge tank.