sorry not with you on this. the old passive is much better for him than the % passive. mainly due to build diversity and becuse its free.
if you have a teemo in your lane, you get bonus mr by farming under your turret without having to recall. this is a big deal. and slowly get more resistant to his poke without even investing gold. youll have resistace numbers by midgame, that you would otherwise only get from it with heavy resistance items like thornmail.
it currently takes a 150 bonus mr and armor to reach a resistance bonus of 30 with the % mechanic. thats really quite a lot. and it means that some of your item slots are always locked up to an item like randuins or some other big resistance item. or youd waste the potential of the passive.
its also to note, that the patch tomorrow will reduce the per rank cap on the resistance bonus. meaning he can put 1 point into it and farm it up to 30. they also increase the bonus per minion back to .3 and even give him 1 resistance for large jungle monsters.
this means its only gonna take up to 100 cs until hes capped out. thats not much.
basically his old w passive is back in all of its glory. he can build tanky and is just as tanky as hes now. or he can focus on damage and is still decently tanky, when he wouldnt be now.