KGB,
In game I played I was busy fighting other players before I could even form stack of similar strength as you suggest. I formed one now just to test it. Attacked Minotaur+Dragon. The battle turned out to be 80% for me. I wouldn't call that surprisingly easy. Even if you won, you would be quite likely to end with assassin, may be one or two orcs and would have be an easy target for attack of some opponent. I remember I once did not get over 90% even with the L3 assassin + 7 units.
I don't want to add razed cities on main islands. I'd like make the centre working. I don't know whether it is somehow possible with the razed cities, but I want to try it. Giants were there because I really thought central razed cities would be used. The idea behind their 80 gold income was that it is more advantageous to rebuild and hold such city in the long-term view. I need to play more games on the map with human players, but now I have to wait until it would be possible