Dwarves can be successfully countered by Orcs (huge boost, rage, which many also consider to be a cheat). If you accept your approach (450 creatures of level 2), imagine the power of the "Rage of the Horde" spell; how many goblins do you think the Orcs will have?

Dwarves can be destroyed by Light Elves if you take the hero Winghael.

Dwarves can be destroyed by Mages if all creatures have level 3 miniatures (and they will, as we will play until there are 450 spear masters); the Mages will cast the Mage's Sign spell and place double stacks of mines and walls and simply shoot down the Dwarves with miniatures that have high initiative and luck.

Dwarves can be destroyed by Demons with the hero Nimue, if they are lucky with the Amulet of Mastery; on the battlefield, there can be 6 squads of Cave Lords.

Dwarves are simply killed by Dark Elves with a relentless rush. This happens on any map, as Dark Elves simply destroy neutral creatures very quickly. On the highest difficulty, their city development is not much different from the Veteran level; everything is very simple, but how are you going to find a huge number of crystals for the Dwarves? You might not be lucky with the mine.

In general, I don't see any imbalance with the Dwarves; yes, it is a very strong race, but it can be countered.

I have already tested the retraining option a long time ago; my friends don't let me play Humans on a large map; rather, training monks into Knights with Isabelle is a cheat; I advise you to try it at least once before arguing, because I am 95% sure of the Humans' victory