how bad was the randuin nerf?

I wouldn't call it bad or even a nerf.

Randuin's is simply no longer a core-go-to armor+hp item. It is now a core-go-to OMG-the-CRITS! item, which also happens to give a good amount of armor and HP.

Basically, if the enemy adc is building IE first item, Randuins is awesome. If not, but the enemy team has something like a Gangplank or Master Yi, same thing.

If none of that, then perhaps Dead Man's plate will give you more bang for your buck. Or Sunfire Cape, or Ohmwrecker, or Thornmail, etc... depending on the situation.

Which I like. I was sick of having all of these unique and cool items that I almost never bought because Randuin's was just so innately more powerful even if I'm too bad of a player to use the active (which now is always a 4second slow btw).

It was a heavy nerf because past mid game it falls off and becomes useless to a late game ADC. The old randuins with 100 more HP and 10 more Armor was way better at reducing damage, then top that with a thornmail and you should be at least lasting a good while against an ADC. The 10% crit reduction is not enough to make up for the crappy stats it gives for being high priced.

So bad that I don't build it on Braum except against Ashe. It's straight to Deadman's plate after SS and Face.