1) Bulwark is the new big MR item, and MR got slightly nerfed across the board. It's the FoN replacement, effectively.
2) Health is much more accessible and easy to get now, especially for tanks. Health counters AP burst almost more than MR does, considering the penetration changes. Grab a mogs and a mallet and you should be completely fine.
What I mean is that if MR is being relegated in favor of just building a massive health pool for every tank, then won't that lead to just as much stagnation as relying on MR too much? This brings up another difficulty I have with the FoN decision: if one of the reasons for its removal was that it was "weird" or had an "unusual combination of effects", wouldn't that be even more reason to keep it in the rotation?
I wouldn't have as much of a problem with the decision if AR items were also being hit (as least that would point to a consistent mentality with the update), but this just seems like tanks are being left with very few options against an AP team or even against one particularly fed AP carry beyond "build more health".
If MR is going to be nerfed, then wouldn't it make more sense from a balance perspective to also nerf AP ratios across the board? Or to make MPEN less effective instead of more?