Heroes 5.5 WarGame Edition - Tactical Edition.

It depends on the faction; each faction has its own strong (expensive) and weak (cheap) tiers.
Specifically for humans, knights are potentially (under the Castle) the strongest tier.

But if the question is whether the growth strength will depend on the strength of 1 creature, then no. If (hypothetically) the knight's strength drops by half, then their growth will also double. That is, the total growth strength will not change; it is already fixed.

Added after 1 hour 33 minutes

as an option, I think nothing prevents making the strength jump between tier 6 and 7 units slightly more significant

Explain using the humans as an example how this should look in relation to the reference dragon. In the format 40:24:15:10:6:6:2 (current ratios, from tier 1 to 7).

Generally, increasing the jump specifically between these tiers will most affect the reduction of discreteness (the value of individual creatures), since currently most tier 6 squads are capable of withstanding 1 hit without losses (if we consider numbers typical for duels). Tier 5 generally no longer possesses this property; there are enough creatures there for someone to die immediately.

Added after 4 hours 3 minutes
Updated descriptions of skills that grant additional creatures:

Pack Leader: 4 wolves per hero level are added to (and continue to be added to) the hero's army.
(cost of 1 wolf - 200)

Call of Darkness: 2 manticores per every 3 hero levels are added to (and continue to be added to) the hero's army.
(cost of 1 manticore - 1250)

Goblin Help: 4 goblins per hero level are added to (and continue to be added to) the hero's army.
(cost of 1 goblin - 100)

Forest Leader: The hero receives +1 morale. 2 dancers per every 3 hero levels are added to (and continue to be added to) the hero's army.
(cost of 1 dancer - 300)

Inhabited Mines: Upon capturing each mine, 5 friendly ghosts settle in it every 2 game weeks, starting from the first (but no more than 25). In the arena, the hero receives 20 ghosts.
(cost of 1 ghost - 300)

Death's Tread: 1 Death Knight per every 3 hero levels is added to (and continues to be added to) the hero's army.
(cost of 1 DK - 2000)

Added after 7 minutes
Specialty changes:

Humans:
Rutger (Swiftfoot): All creatures in the hero's army receive +1 speed.
Godric (Ideal Knight): The "Prayer" ability is strengthened: the bonus increases from +2 to +3. The hero spends 1 less mana to cast Light magic spells.
(prayer no longer provides an initiative bonus)
Frida (Captain of Knights): Damage dealt by knights in the hero's army is increased by 10% per hero level.
Alaric (Archbishop): 2 monks per every 3 hero levels are added to (and continue to be added to) the hero's army.
(cost of 1 monk - 600)
Valeria (Holy Hammer): Every time the hero casts a Light magic spell on a friendly squad, there is a 2% chance per hero level that the "Righteous Might" spell will also be cast on the squad.

Elves:
Wingael (Swift Fighter): At the start of battle, the starting position of each squad in the hero's army on the ATB scale increases by 2% per hero level.
Anwen (Sword of Silanna): All Forest Union creatures under the hero's command deal 3% more damage per hero level to a sworn enemy on any attack (even if a critical hit does not trigger).
Vinrael (Windrunner): The "Haste" spell is strengthened. Its effect increases by 5% per hero level.
Tieru (High Druid): 2 druids per every 3 hero levels are added to (and continue to be added to) the hero's army.
(cost of 1 druid - 600)
Dirael (Hive Queen): 2 fairies per hero level are added to (and continue to be added to) the hero's army. The "Summon Wasp Swarm" spell is strengthened. Damage increases by 5% per hero level.
(cost of 1 fairy - 125)

Mages:
Jalib (Spell Turner): The hero receives +1 luck. The "Magic Mirror" ability is strengthened, so that when triggered, it always reflects spells toward enemy squads.
Nura (Mystic): During battle, the hero restores 1 mana per turn for every 5 hero levels.
Ora (Wind Speaker): The hero's initiative is increased by 1.
Cyrus (Stormcaller): Heroic Air element spells cannot be deflected. The hero learns strengthened versions of these spells in addition to the regular ones, which deal 150% damage for 200% mana cost.

Dwarves:
Helmar (Eternal Warrior): 3 berserkers per every 2 hero levels are added to (and continue to be added to) the hero's army.
(cost of 1 berserker - 300)
Wulfsten (Oakshield): Squads in the hero's army receive 3% less damage from ranged attacks per hero level.
Tolgar (Rune Artist): The probability of the "Completed Rune" skill triggering increases by 2% per hero level.