Justice is a fan-made global mod.

The Swordsmen in the seventh installment are a tribute to similar units in Heroes 2, placed at the highest tier.

But those Swordsmen, at least by name, hinted at magic (Paladins). And, in fact, they multiplied in large numbers and were closer to the previous tier than to dragons.

In my personal opinion, as an exception, "minor" units could be given higher tiers. For example, the Dark Elf Witches, purely from a lore perspective, are not ordinary citizens, but rather matriarchs who essentially manage the clans. They can be placed at their level (especially since they are among the weakest at that level).
Another question is how huge and quite impressive Hydras with regeneration ended up on tier 5. Here, I fully support moving them to tier 7.

In the absence of Hydras, it could be done, with some stretching and an increased growth rate (for example, up to 3). But a Hydra is definitely no less than half a dragon or a Wyvern.

Well, why not? Heavy cavalry could be Tier 6. The Death Knights are definitely like that.

Specifically, Death Knights can be tier 6. But regular human Knights are too simple for tier 6. In Warhammer, 1 dragon costs as much as dozens of knights, and here they are simply placed on neighboring tiers. And yet, a dragon eats horses for dinner, while here they took a large horse, put it in armor, put a man with a spear on it, and voila - a couple of these guys are already a threat to a dragon.

Also, monks are probably another case - precisely because of the training, as you described. It's hard to imagine that any man, even for money, could be turned into a Hydra killer... And Paladins violate logic for the same reason. In general, human training has always been specific in terms of lore.

Of course, they violate it - that's why Knights don't belong on tier 6. Although, again, with some stretching, if you weaken them and increase the growth rate from 2 to 4, they could be left there, but why, when there is such a magnificent monster as a Griffin for tier 6.
Moreover, if I'm not mistaken, a Griffin also enjoys eating horses, and if you add a knight to the mix, the very same one who was plowing the land yesterday...