the Juggernaut update still far surpasses the Tank rework since it went beyond just the champions that were reworked's balance states
so did the tank update, nerfs to health across the board have had echoing effects on bruisers, with a lot of them taking a dip in power that Riot now has to take their time compensating individually, unless they happened to benefit massively from the AD changes
Furthermore, it's not like they all do it in a similar way.
the end result is the same, so who cares? Sejuani can could engage from a distance, too, Sion and Malphite do it as well. How you do 'X' thing slightly differently should not be considered a niche; a niche is having strengths that others, or at least very few others, have. And this, funny enough, is one of the things that the Juggernauts do better than any other subgroup.
As stupid as I think Poppy is she's a good example of an actually niche tank because of her W, E and R serving as a reliable hard-stop to dashes. She functions excellently as an anti-mobility tank, even if I think she's still too good against immobile targets. Other tanks can interrupt mobility with their own displacements, but most of them can miss where Poppy can't, and they don't usually have 3 opportunities to stop a Lee Sin flanking.
Ignoring her now terrible animations and mediocre balance state, Sejuani's rework is especially shit because her 'niche' isn't in her control. You have to beg soloQ teams to pick melee champions so that you can actually be a stun bot and not just a chogath-tier meat shield when it's time to fight 5v5. And that's all she has now; stunning people. Previously she was far closer to a very tanky diver, or at least a hybrid, because she followed a similar pattern as Hecarim but with spammy slows attached; ult onto the enemy team and then beat down the closest carry, basically a semi-carry herself. Old Sejuani had far more skill expression in decision making; because of her nature as an AoE-heavy tank with high DPS she had to choose between running one person down or spreading her E stacks to as many people as possible to slow all of them and set her team up, as well as deciding when to ult. New Sejuani has lost this; you'll press E as soon as it's available, because there's one outcome; one person will be stunned. R is the same way; now with piss-poor initiation, R is only used as a combo reset to double her stun time. The only thing I actually like about the rework is that she can kill Scuttle in 3 seconds instead of having to chase it around the river for 10.