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Ah, balance, balance...
Making health percentages like that (as Javdet wrote) isn't a good idea, in my opinion... especially since it won't affect Brog, but for the Miner, a 3% health bonus from 5/6 Trog units is what? It turns out you'd have to give at least 1 health point... then there's not much point to these 3%.
It's simpler to either give a fixed health bonus or a smaller percentage, for example, 10-15%. For the first level, this would be about 1 health point, and for other levels, it would be approximately (1-2) * level of health, for example, for an Ufretin, 15% of the Dwarf's 20 health is 3 health, and for Brog, 15% is 10-11 health.
Another option is to give special units a percentage of their own health equal to their level (minimum 1, rounded down) or equal to level * 2. Then Brog and Shakk would be as strong as they are now, but only after reaching level 25, but this would weaken other special units... although Vale and Tirasu would be almost as strong, only with 11 health instead of 12 for each of their subordinate units.
In general, all these arguments are largely based on experience, which is why imbalance occurs... because with special units, you immediately have both quantity and quality.
I have a suggestion on how to reduce/balance special units, not too drastically, of course: give special units 3 stacks of level 3 units instead of 2 stacks of level 3 and 1 stack of level 1. Then the Miner would be in trouble not only with the arrival of Lore, but also with Ajiki, and the Elves would become stronger with Ivor (Vik already said that the Elves are weak in terms of attack power in the current situation, as is the Tavern). For Humans, Edrick would be interesting, especially if the Griffin Nest is separated from the Barracks and Blacksmith. And you could also suggest separating Mages from Golems and, as an option, adjusting Josie's skills to create another decent hero in the Tower.
In general, I once had the idea to make all heroes have 2 stacks instead of 3, and to return the army of 2 heroes in the Tavern. This would look more reasonable... than Vale with 30 Archers at the start or Shakk with over 100 Trolls.
By the way, I would like to balance the Dwarves, Ghouls, and Golems. Even as support units, they are very ineffective because of the need to move them to important battles... Ghouls are fast, but they are fragile and there are always few of them, as they are all used as decoys against the Grem.
I suggest giving 1 point of maxuron to Dwarves, Ghouls, and Golems, and weakening Ghouls in terms of health (-2), but increasing their growth in the city (+1) and increasing the number of Ghouls at the start for heroes (+1). Do not change the adventure value of Ghouls (since damage + and health -).
A separate word about the Tent skill. It's better not to give it to anyone except special units for now, because a script has already been made for the Tent, which will heal not 1-x, where x is the level, but will heal a-b, b-c, c-d, i.e., not from 1, but from the end of the previous range, and then "imbalanced" will be the Tent users with a group of 5-7 level units.
Regarding experience, in my opinion, it's better to play without it... the differences are too large, especially the damage bonuses are significant... and the percentage of health for special units with unit experience is generally illogical.
I believe that with experience, the imbalance of special units in terms of monsters is much more noticeable.