Did...did you even finish the story?
Dude gets weakened, captured and tortured for weeks. Its not the imprisonment that rattled him, its the loss of power and viewing himself as a failure. For someone who had been told his entire life that he was the Dark Lord, that he was going to rule everything, to have all that taken away...twice, first with being sealed and then by being captured. That's enough to break someone.
Notice that once the seal is broken and he chooses his Bride, any weakness is gone and he goes full out Dark Lord. Like even more than he was earlier in the game. This is someone back at 100%
Yes, I did.
Why do I get a feeling that you are talking about some hypocrating isekai teenage, who, suddenly, found out that being a hero is not about looking cool and having a harem, and he surrounded not by NPC, but actual leaving and breathing people that bleed, lie, cheat, betray and can stab you in tha back?
As well, let me point out, that defeat and imprisonment was not Dark Lord "first rodeo". He already experienced that sort of thing, being even crippled in an all out war (his first defeat), and at that time, he was not scared by the prospect of been sealed, for an
unknown amount of time, when
you actually can do nothing but wait, I may add, and he did not cried his ass out. And what about now (at the time in witch game takes place)? If anything, he already should know, from experience, that, sooner or later, even if much later (he IS immortal after all), opportunity will come. On top of that, he was
JUST imprisoned,
NOT sealed, so he could plot, corrupt, deceive, slowly build up his influence and do so much more,
IF he would take some time out of crying and self-pitying.
Again, we are not talking about insecure boy who's daddy did not bought him a pony on a birthday, we are talking about freakin Dark Lord, who should have come through hell, low and above, to build his Empire (the first time), since only through power, wit and decet he could build something like that in an "no man's land".
That was the lamest turn around! Ugh, it was so disgusting...
Damn, when there was no apparent and immediate way out of his situation, he was ready to wag his tail and lick the boots of Matriarch. But who would care about that if, in his mind, he would be seething with anger and plotting his revenge. But no-o-o, he wasn't! He was really ok with turning in and becoming his Arch-enemy lap dog! And when, suddenly, he was rescued, he immediately switched out and started to act all high and mighty.
Talk about a man with no conviction...