In my opinion, heroes like Solomyr, Luna, Ciel, and others are only relevant in the early stages! Later on, they are no longer needed! If you find Solomyr, level 15, for example, in a dungeon, his secondary skills will most likely be spoiled by some kind of mysticism or training, and his primary mage stats will also leave much to be desired... so there's a 99% chance he won't become a "powerhouse"! And he probably won't be able to take down anyone with his Chain Lightning anymore, because the hero who broke through the dungeon's defenses will have better stats, secondary skills, and spells, and his troops will be stronger...
Isra and Vidomina will only be useful to Necromancers, but what is the probability of finding one of these two in a dungeon, and at a decent level, while playing as a Necromancer???

But if, by chance, a situation arises where the freed hero can be somehow used, then breaking through the defenses will be justified, as the strength of those defenses often reaches the level of the defenses guarding some relic!!!