Diffusal Blade's single target dispel has been transferred over to Nullifier's active. If you really think about it, it's a damage item that dispels and slows, just like how Diffusal Blade was before. But mostly, only Agi carries would build Diffusal blade, and it's rare sight for int and str heroes to do it unless the game is totally unwinnable without any dispels.
Now, the offensive single-target mechanic can be built by just anyone else without preference for agility heroes due to agility stat build up by Diffusal Blade. I remember watching a team–Dark Seer and Omniknight offlanes. Dark Seer's carry was having a hard time surviving the fights, and so he built items to ensure his survival. But that means that no one could purge off Omniknight's Guardian Angel. Since Dark Seer's carry was PA (from the patch before Blur had an active), completing BKB was not enough to win the fights. It made PA survive the fights but they could not win it. Then Dark Seer was found to be carrying an Alacrity Blade and the casters were like ???? Then Dark Seer was relegated to the role of purging off the enemy's GA and suddenly, they could win fights. At the end, Dark Seer's team won. But a Dark Seer carrying a Diffusal Blade was a bit of an eye sore. And ultimately, the item was built to offensively dispel statuses from the pesky Omniknight.
Nullifier solved that "eye sore" problem. But since its advent, it has been slightly overpowered. At first, it muted items for 5 seconds. Getting touched by Nullifier's active was a sure kill to heroes that are so item-dependent. Tinker and BKB heroes to name a few. The name of the game them was who jumped who and who activated what item first.
But now, it's been reworked to "continuously dispel" any positive buffs off the targeted hero just like how Shadow Demon's ultimate works. I've been in too many games as a support and then die to nullifier.
It's not even a game of pre-empting or predicting moves anymore. Since nullifier continuously dispels, there is no "right time" to press that Ghost Scepter. Press it first BEFORE the enemy jumps you, it gets dispelled anyway. Press it AFTER the enemy carry jumps you, and now it's the continuous dispel mechanic that's at work, ultimately dispelling it too.
What's worse is that multiple common defensive support items are ALL dealt with by Nullifier. Nullifier is just one item, but surely, it dispels a lot of things that your everyday support hero will have. It dispels:
(1) Eul's Scepter
(2) Aeon Disk
(3) Glimmer Cape — Glimmer Cape has a delay before the invisibility kicks in. Before that, even if the carry who has the nullifier has no detection, he can still easily kill you no problem
(4) Ghost Scepter
(5) even the "push" active by Force Staff. If you get nullified, and you attempt to create distance from your enemy by using your Force Staff, the "push" will get dispelled and you will not propel into the direction intended.
That's just 5 common items built by supports. But down the line, it even dispels Windwaker, Crimson Guard's shield, Drum of Endurance buff, Ethereal Blade, and of course, all dispellable abilities in Dota. It seems like BKB is the only thing that could deal with Nullifier's active. But that's a difficult thing to ask of a support. Most of the support items create not only the escape/save functionality but also it makes sense. It provides stats, mana pool, mana regen, etc. But BKB is a selfish save for a support. Even then, the continuous dispel mechanic remains undispelled in spell immunity. Weak dispels like Lotus Orb and Oracle's Q will not dispel Nullifier's active. Strong dispels like Legion Commander's W or Abaddon's W, surprisingly, will still not dispel Nullifier's active as well. You'll discover that once you are touched by Nullifier's active, even if you press BKB, you cannot gain new buffs. You still cannot use Force Staff or use Glimmer Cape bec. Nullifier's active still persists through BKB. Imagine if your enemy team has 2-3 Nullifiers. Then it's just impossible.
My suggestion is to lower the CD of Nullifier, make its projectile faster, can still dispel all positive buffs, but remove the continuously dispelling mechanic and can only exert its dispel once and lower its duration so it's not 100% up time with the lowered CD. If you think about it, Shadow Demon's ultimate is only just 1 tier above Nullifier's active in that it pierces AND persists through BKB. Nullifier only persists through BKB, but cannot pierce BKB. Which is a weird mechanic altogether? LoLs.