In your opinion, which faction is the strongest in Heroes 5? Let's discuss the advantages and disadvantages of each faction.

In my opinion, on XL maps, the Dark Elves fare the worst. The more troops there are, the weaker Chaos Magic becomes (unless the map is randomly filled with +1 magic), and the stronger Light and Darkness magic become. Their super ability isn't the best either; the Orcs and Elves have better ones, especially on large maps. Humans will have time to train (peasants will pay for themselves by converting into Arabs), Inferno will simply consume all the mana, the Academy will be filled with artifacts, the Necromancer will have skeletons measured in kilograms (Implosion + Boots of Grounding + Arcane Wave won't help), and the Elves with Eternal Luck and Sworn Enemy will be terrifying. As much as the Dungeon is great for medium-length games and maps, it's weak on XL maps.

Based on your post, it seems like the Dark Elves will just sit and watch as all the other races strengthen themselves. On an XL map, I will persistently search for enemy heroes starting from level 10-12, only being distracted by truly worthwhile things. Even if I don't get very lucky with the starting position and development (in terms of time), a well-developed level 12 Dark Elf hero is capable of tearing apart a hero of any race that is 3-4 levels higher. I'm not taking artifacts into account, as most people do when describing the advantages of their factions; I'll just say that with the necessary artifacts, the "dark-eared one" becomes a terror on the map. P.S. On an XL map, in my opinion, the Dark Elves' strategy should be based not on focusing on their own development, but on preventing the opponent from developing (IMHO).