On my youtube channel people told me not to abuse necromancy, and didn't mention angels at all. You cite a lot of experience though; what quantifiable evidence did you have that archangels were too strong in those MP games?
Uh, it was a long time ago. 10 years. What I can remember... it isn't OP against AI, but against human players. If you have humans clearing the map they usually do it without or with minimal losses (clearing the mobs, mines etc.), following a strict build order and generally avoiding figthing against enemy heroes, except if you catch the "noob resource gatherer heroes" or the "secondary hero".
If it's free-for-all (as it usually was, 1v1v1 or 1v1v1v1 or 1v1v1v1v1 or even more), diplomacy was either "dogpile one", but usually two or more camps arose. The first clashes of two strongest human heroes are always devastating, usually resulting in loss of many weeks of units. The defenders obviously had the benefit of having a weekful of units more, except if you grab your weekly units fast and rush the enemy.
As you point out, Archangels at this points are not really a factor. But it also doesn't matter, because the Castle guy doesn't even employ them yet. He just tries to kill as many units as he can, surrenders, then immediately buys back his hero, picks up his few Archangels, splits them into two stacks and starts clearing your territory. No matter what you throw at him at that point, your lands are empty and ripe for picking.
Correct me if I'm wrong, but if I remember correctly, Archangels are always first on initiative, they are also fliers and have a huge (if not max) range for flight, so your archers get locked down immediately, while your "initial clash" surviving forces are usually the "lower attack, stronger defense" units, which is easy win for a twin Archangel stack resurrection abuse.
As soon as the Human Castle player gets a hold on merely
one other player's land, gems and gold stop being a problem.
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The difference between Human Castle and other castles is that the human castle can do well without it's Angels. While at the same time, for comparison, Rampart cannot do battle properly without Dragons. Castle has everything it needs to control a human-controlled army - fast Cavaliers to rush enemy archers, strong Paladins and some ranged support in archery units.
Tower and Dungeon can pull this (initial clash without top tier unit) off as well, to some extent, but their inital expansion is slower (no good archers early game). Solmyr (Tower Wizard) or Alamar (Dungeon) can help help, but it still doesn't beat the initial expansion of Castle with Orrin (to be secondary hero) or Rampart.