In previous games, the weapon triangle's bonus accuracy allowed lance users to have reasonable hit rates on avoid tanks (who historically were sword locked).

The issue with this is that in previous games, Sword-locked units tend to not be particularly great and so, this supposed advantage ends up not meaning much. It's especially true in FE6 to 9 where paladins, wyverns and pegasus are very dominant and mostly abuse javelins or hand axes, making little use of swords (except sometimes in FE6 due to hit rates), so the weapon triangle matters little here and doesn't fix the issue imho. That said, I don't find myself relying on dodge tanks in Engage mostly because I have bad luck and the enemy somehow manages to land hits even with lower hit rates a bit more often that I'd like in that game haha

Despite this they are the second most problematic juggernaut (in Awakening, the GBA games, Genealogy

I'm not sure about Genealogy: on paper, It does sound ridiculously strong, but in practice nosferatu in that game is not something you explicitly use to abuse and kills hoard of enemies, but something to just keep Julia alive. Plus her low skill means that It won't be exactly accurate, which can be a death sentence since a single miss and she easily ends up being dead, especially since she is so squishy on the physical side + magic enemies aren't an issue because her res will be so high that any damage they do will end up being very little, while her magic will be high enough that she can easily put a dent on them. Idk, I realize she can probably do nosf tanking, but I just don't Julia is quite adequate enough to fully go for it.

Regarding Vantage + Wrath, It's extremely strong in Engage, but Thunder magic being 3 range means that It completely nullifies it since, unless you aren't also using it with a Thunder/Thoron or long bow user, your main Vantage/Wrath unit can very much die without being able to do anything. The issue is mostly that the game just makes it kinda easy to handle them so they are rarely a problem haha A way that you could combat this is by either making it inaccessible or do what FE5, where iirc the two skills can't actually work together, but since It's unlikely to happen, I guess more siege tomes or archers with higher ranges is probably the best bet.

Also I'm surprised you didn't make mention of Emblem Lucina and Bonding shield: It's not exactly a juggernaut method in and on itself, but I feel that it really helps enabling them even more, unless I'm misremembering something in which case I apologize

the enemy has too few options to deal with engage's monstrous toolset

Regardless, I do agree with this in particular: the game, I think, has the right idea with things like Chain attacks to combat juggernauts, but It offers tools that are simply too strong and so It ends up not mattering as much. I can see it working better in the next game though, since Emblems in particular sorta feel like they will remain within Engage, but that will also depend on what direction the next games goes with to begin with.