Gnar's Passive - Nerf or Fine As Is?

So I just played against a Gnar in the top lane. Every time his passive popped he would gain a massive amount of HP and resistances. Yes, I understand that it is his passive, however I believe the amount of free HP and resistances given is a little high given that other passives of similar veins have already been nerfed to level the playing field. His base stats are fine, I believe, and he is a strong pick in the top lane with his poke, mobility, and relatively intuitive crowd control.

30 + (40 x Gnar's Level) is a little high. When dueling him at level 6 in the top lane once his passive pops he immediately gains 270 HP and 12 armor and magic resistance. At level 11 this becomes 470 free HP and 22 armor and magic resistance. Level 18 brings 750 HP and 36 armor and magic resistance.

If one looks at a similar passive in Shyvana, she only gains 5/10/15/20 armor and magic resistance (Doubled while in Dragon Form) but she doesn't see a massive health gain unlike Gnar. This is only exacerbated as most Gnar builds contain health, armor, and magic resist as it is. While this transformation does is not exactly on demand like most ultimates, which provides some counterplay and relief for most ranged top or mid lane champions, with the health regained from the passive permanent upon leaving Mega Gnar and great kiting potential it seems a bit much. Even Renekton and Nasus only gain 200/400/800 and 300/450/600 HP respectively and this is their ultimate.

I believe that the armor and magic resistance portions would be more balanced if the health was nerfed slightly to 30 + (28 x Gnar's level):

Level 1: + 58 HP and 2 AR/MR Level 6: + 198 HP and 12 AR/MR Level 11: + 338 HP and 22 AR/MR Level 16: +478 HP and 32 AR/MR Level 18: +534 HP and 36 AR/MR

These challenges make Gnar players use their passive intelligently instead of a free health boost in lane, and when you're dueling them it makes the huge stat boost less oppressive while keeping it in line with other health/resistance gaining abilities. No reason why one champion should get Dragon Form Shyvanna's resistances while simultaneous getting a near Renekton-like 750 HP boost in just a passive. I believe that Gnar is strong currently and is a fun champion to master, but I do think that he could be toned down slightly while still maintaining a strong presence in the top lane.