Heroes 5.5 WarGame Edition - Tactical Edition.

It's not difficult to come up with a name, even if you draw exclusively from Scandinavian mythology/culture. What's the problem with calling them Jotunn, Aesir, or Vanir? Or Huscarls, if you want something in the style of Jarls and Thanes?

Scandinavian titles won't sound right.
Aesir is too refined a name; it doesn't convey the raw power of a giant.
Jotunn is the most interesting option of those listed; it needs further consideration.

I suggest giving the Earth Element-aligned Dragons immunity to Earth magic, and the Mind Element-aligned Dragons immunity to Mind magic.

Mental immunity already exists for Titans and Berserkers. Adding more mental immunity is debatable, again, considering the goal of minimizing the number of abilities and maintaining the uniqueness of the Titans within their tier.
The same applies to Earth magic; if there were Stone Dragons, it would be a different story. In other words, the ability lacks support from the visuals and gameplay; and if we try to align it with the official lore, we could end up with Tier 5 Vampires, and other "lore-based" changes in magic, etc. (I don't see any other compelling arguments in favor of including these immunities).
Azure Dragons already have a good immunity – to Death. A second one here is redundant. On the other hand, Elves don't work with Chaos (Druids in the new release will also be without Chaos, only native Light+Summoning), so immunity to an element for a non-Chaos Faction is strange. Elemental immunities exist for mage creatures, Dwarves, and Demons – all of them are Chaos Factions, meaning they can throw immune units into the fray and blast them from above along with their opponents using area-of-effect spells.
Again, I would like to point out that Golden Dragons, and especially Azure Dragons, contradict the lore themselves. The latter are definitely not related to Earth; Golden is closer to the Solar Elrath, and Azure is closer to the Celestial Ilath.

Added 7 hours 2 minutes ago
I think it would be better to give Dwarves a racial bonus of 1/2/3 random resources (excluding gold) for each level, including previous ones? The idea is that these are the resources that the Dwarf will spend on using runes in the breakthrough (compensation for resource loss). On the arena, give corresponding bonuses only for levels exceeding 12 (the basic upgrade level).

Another question: what to do with the racial bonus for Mages, since it is also tied to the artifact forge; if there is no forge, then the racial bonus is 0.