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

Of course, it can be removed; I wrote that it cannot be dispelled, and that's important. A dispel can be easily cast in half the initiative, but Berserk cannot.
Out of habit, we cast Berserk so that it cannot be removed, at least until the first turn of the unit. Then you remove it, both turns are spent, and only one benefits. Of course, sometimes it's useful to cast Antimagic or Vampirism.

That's correct, but the Knight won't be able to hold out either. The Knight usually has one stack that has just finished training (either Imps or Paladins), and one of the immunities is immediately cast on this stack, if available. In the worst-case scenario, the Knight will receive one hit from his own units. This will interrupt the tactic.

Even closer to 56%, but how many races do you develop Light and Darkness simultaneously? And do you develop them simultaneously for the Knight, the only one in the guild who has Light and Darkness? I don't think so, so the probability should still be estimated at 33%.

No. I definitely don't develop two magics at the same time. Moreover, I will first level up the hero to level four, and only then will I start developing magic. If I see Antimagic, I will definitely choose Light; if I don't see it, I can level up one more time and see if Vampirism is available. If resources are scarce, there are two options: risk and develop Darkness, or give up and develop Luck and Resistance (if there are +10% boots, that's also an option).