The only thing that BC needs is for the CDR to be unique, just like it is everywhere else, maybe the flat arpen too, but that's not really a big deal. Liandry's is fine as is; I'm pretty sure the only champs who can get the full 10% off of it are Anivia, after she gets her ult, and Karthus. Of course, that's assuming you have 0 MR.
There could be others, but what's required is 1) a 3-second slow, stun, or snare (or perfect chain thereof), 2) a single-target, non-DoT, magic-dealing spell, 3) the removal of all your MR (e.g. Abyssal Fidd is nearby when you have 0 bonus MR), and 4) your hp regen is reduced to 0. Then, and only then, will Liandry's deal a full 10% of your health over 3 seconds. If any one of those conditions is not met, you're looking at as much as an 80% reduction off of that.
For example, if there's no shred around (not pen mind you; has to be shred 'cause items don't use pen), and/or you have even one of the +50 MR items (or have it naturally), you've cut the damage by 40%, which means if all of parts 1, 2,& 4 are in place, you'll only take 6% of your hp as damage from Liandry's. If you have decent regen, and most champs naturally have on the order of 15-20 hp/5 w/o masteries or runes, that by itself will offset 10-12 hp lost, which is 1% of most squishy champions' hp.
Coupled with MR, that puts Liandry's down to only 5% of your health. Now, if you are not slowed/snared/stunned for the full 3 seconds, every second you're not slowed only deals half as much damage; with a little MR & regen (e.g. one Spirit Visage) you can take as little as 2-3% of your health as damage from Liandry's. Finally, if the final spell that hits you is a multi-target, aoe, or dot, that will cut Liandry's down by half again, for a base of only 2.5%, further reduced by MR and regen to as little as one half of a percent (0.5%) of your health as damage. Get a Warmogs + SV and your damage could be effectively 0 (because Warmogs gives you back 1.5% of your health over the same time period, increased to 1.8% per 5 or 1% per 3 which nets you positive gain).
So, quit whining about Liandry's, it's hard-countered by Spirit Visage: buy one, get tenacity or don't get stunned, and don't worry unless your opponent is Karth, Aniv, Vlad, Kass, or Brand.