Theory and Practice

That's too much. ))) At least 45 skills are needed. )))
There's just a special major skill for the Hand of Death, which allows you to cast it even without Grand Magic of Death. It drops on some maps. PS rarely does without it.

Well, regarding the minimum – I specified that it's for a large map. And on a large map, I think it's quite possible. Although, you don't even necessarily need to level up magic – it's enough to find some kind of Chaos Wand, like a Fireball.
Or – Chaos Magic – even an Expert level is enough (6 skills – maybe it's enough with Universities and Altars) + Lightning... In total, we get a Guildmaster: at least seven skills in Nobility and Scouting + 6 skills in Chaos, totaling a level 20 hero when leveling up purely through experience, minus levels for Altars and Universities, and there he is!... Level 13-15 is quite realistic. By that level, Lightning will deal about 300-400 damage.
You can also use the Order – Advance + Ice Bolt.
But the combat wand option is also good – you don't have to be distracted by leveling up, and by the endgame, the wand will also have considerable killing power.

Draw your own conclusions... And I will definitely check it – all this is just theory.

P.S. And I'm hearing about the Hand of Death major skill for the first time:( I've never seen it:(
By the way, can you tell me exactly how the Guildmaster's ability works – I don't remember whether it reduces resistance by a factor of three or by a third:confused: