The final campaign – “Even Angels Cry” [7th campaign – 1st mission].

concurent, up to level 4, it's only a million experience points.

Well, it's more like 4 and a half, not 4, and definitely not a million. But I've already maxed it out to 5, I just remembered it in passing. Yesterday, I was leveling up Arachne to 5 on Angels. There's only a little bit left.
Well, I don't know, I don't know, I'm not really an expert in Heroes, and I don't need to brag, but the fact remains that the final missions are just a bloodbath.
But I suspect that's because I set some expensive dynasty features, including those from the gold and platinum tiers, and hero settings that significantly simplify the gameplay.