The map is unreal, generated randomly.
Lots of castles.
Lots of gold.

1) How strong are the Humans? Can they compete with Necromancers and Orcs?

If the random distribution of your own and enemy castles is standard, then Necropolis will have 3-4 times more troops just due to castle reinforcements. If the Mentor skill is not banned, the Knight has no chance, even +20 Paladins per week are insignificant.
Against the Orc, use Offensive Guard + Darkness + Inspiration to take down Cyclops before any reinforcements arrive. The chances are good.

2) What are the best and worst opponents for Humans?

The best is Tower, universally good for everyone.
The worst are more difficult to determine. Necropolis, Magic, Demon (if Imps nullify mana). However, all the others are also not a walk in the park.

3) Do Humans need logistics? (considering "huge" and "incredible" maps)

If the game doesn't have pre-arranged agreements like "we'll meet in a year at a designated location," then logistics are always needed, for everyone. Especially if a Mentor is found on the map.

5) Describe the tactics against Gnomes. (considering "huge" and "incredible" maps)

The Knight has very limited tactical diversity, only variations against Orcs. Quickly eliminate everyone with cavalry and prevent them from casting runes.

6) And is it even possible to defeat a Necromancer on an incredible map 1 on 1?

8) Can you bet on converting Monks into Knights in a game against a Necromancer, and win? (considering "huge" and "incredible" maps)

Without restrictions on the converter and Mentor, the Knight can only win with Sandro's Cloak, two magic skills, and even then it's difficult.

Why is Keen Intellect so good?

We need to analyze specific examples. For example, against Orcs, it greatly increases the chance of reaching Shamans and casting something tricky from Darkness, or using Empathy from Griffins to inspire Paladins and defeat Cyclops.

I would like to additionally object to some other very controversial statements.

Orcs become weaker in the late game, armies grow, damage increases many times, Rage is dispelled faster = Orcs have no advantage.

Damage increases strictly proportionally to HP, therefore Rage is dispelled at the same rate.

Haven is the most protected castle from Darkness magic in the game. As many as two units (Paladin and Inquisitor) can remove control effects + a hero with Light magic.

After Orcs and Demons, it is the least protected.
-Control is cast on Paladins, or they need to be left under Anti-Magic, i.e., without buffs. + spend the turn of the strongest stack.
-Have you tried removing hero spells with Inquisitors in the late game? And how did it go?

It is quite possible. Necromancers are not the strongest race in the game. Unless there are many castles on the map.

In the late game, as described by the author, without additional restrictions, the Necromancer is perhaps the strongest race in the game.