You can defeat them if you fight them in castles and use Might and Magic spells. In open areas, your chances are minimal. Also, before fighting the strongest hero of the Tower, I removed black dragons and harpies from my army. + recruiting creatures in castles helps a lot. Thanks to this, I managed to gather a combat-ready army before one of the Tower heroes attacked me. The Tear of Ascha is given to you for a reason.

Yes, probably, you can defeat any opponent. Especially if you use cheats :). My question was: why is the game version called "light" if only a very experienced player can complete it on almost the lowest difficulty level ("Warrior"), and even then, only with unlimited patience and incredible luck - the enemies attack me precisely when I am in my castle. By the way, I wouldn't have been able to handle the main forces even in the castle: 150 Black Dragons will fly over the wall in 1 turn. Since I didn't see Sandro's Cloak anywhere, that would be enough... All I managed to do without too many fatal losses was to capture 2 (!) castles. Of which, only one is fully rebuilt... And even then, as I wrote, Marbas immediately blocked my way to the castles, which cost me all my riders and half of my harpies. Maybe I'll try it on Recruit someday, but I suspect there won't be any difference in the Dungeon. Also, the enemy heroes were very surprising - initiative is TWICE as high - without any artifacts, luck and morale don't care about the Cloak of Shadows and the Ring of the Broken Spirit, etc. Maybe, after 20 years of playing HOMM, I'm still too bad a player for this map :(