I agree with this, and I think part of the problem comes from how all-encompassing the vanguard subclass is. It's technically meant to designate offensive tanks, but there is such a large variety to what offensive tanks can do, i.e. initiate, disrupt, lock down, and so on, that trying to make newer vanguards do all of that at the same time has led to very samey designs with far too much hard CC. In spite of his once-legendary crowd control, Nautilus is mostly focused on single targets, and cannot effectively disable multiple opponents at once. By contrast, champions like Galio, Zac and now Ornn can continuously lock down multiple enemies at a time, while also possessing more mobility, more damage and comparable reliability. Whereas Nautilus once set an upper limit for CC that was considered undesirable to exceed, modern vanguard designs have set an upper limit that is practically impossible to exceed, short of giving newer designs AoE knockups on every ability, including their passives. This also creates a pretty crowded design space where it's difficult for newer vanguards to express themselves in a unique way, and has also largely contributed to an environment where melee champions cannot operate without spending most of their in-combat time getting hard-CCed.
In order to remedy this, I think we need to start making a distinction between lockdown tanks, i.e. champions who are very good at locking down one target and one target only, and disruptor tanks, i.e. champions who can affect multiple enemies at a time without necessarily outright disabling them. In order for disruptor tanks to be valuable without laying down as much crowd control, Riot needs to start looking really hard into interesting debuffs: Amumu's magic damage amp is a good example, and Ornn's Brittle effect would be similarly good if it didn't amplify CC on a kit already loaded with knockups. Historically, Riot has shied away from debuffs because stat reductions didn't feel fun or impactful, but that still leaves plenty of room for other interesting effects, such as Stoneborn Pact's healing rune, damage marks like Leona or Ornn's, impairments to select effects like healing, shielding, projectiles, basic attacks, and so on. In the case of disruptor tanks that are part-juggernaut, which I think is the case for Sejuani (or, at least, pre-rework Sejuani), part of their disruption could be expressed through strong damage of their own. In essence, a lockdown tank should draw focus from the enemy team because they'd be taking one of their allies out of the equation (which should encourage them to focus priority targets like the mage or marksman, rather than the enemy fighter or tank), whereas a disruptor tank should draw focus from the enemy team because otherwise they'd keep putting them at a constant disadvantage by messing up their capabilities.
To me, one of the most fundamental aspects of a tank is that they want to take damage. No matter how much crowd control you pile onto their kit, if a tanky champion does not care whether or not they're being focused, they're not a tank, they're a fighter. This is why I think most modern vanguards like Galio, Maokai (who shouldn't be a vanguard in the first place), Sejuani and Zac are actually just CC-heavy bruisers, because literally none of their offensive power is conditional upon them taking damage, and many of them apply so much CC that their gameplay ends up focusing on preventing the enemy from applying damage at all, rather than drawing it upon themselves. This is also one of the reasons why I think the update worsened the confusion between fighters and tanks, because their playstyles ended up becoming even more similar. In order to create truly successful tanks, I think Riot needs to look at them with a completely new mentality, and needs to start making their power conditional upon drawing threat from the enemy team. In the case of Wardens this is likely going to be easier, as champions like Braum and Shen are designed to throw themselves in harm's way in order to block damage for their allies (though I feel Shen's W might need to change in order to redirect damage to him, as it currently anti-synergizes with his innate and forces him to have sub-par stats), but in the case of vanguards, that means they need to start giving the enemy team more room to actually fight back against them.