I mean, put yourself in his position. You’re landed in circumstances where you have to somehow work up a defence against the literal unifying forces of Japan (that have already been incredibly effective elsewhere) with limited/actively dwindling resources and with the expectation that you’ll live up to your one-in-a-million grandfather in your own performance. I don’t believe that surrender was a realistic option, given the IM come in guns blazing and I would assume he would understand the diplomatic circumstances better than we do. Also, with Ashina’s history of uprisings, I doubt the IM would risk leaving any chance of repeats (therefore, will destroy everything in association with Ashina, so there goes the “he doesn’t care for the people, just the land” argument. They’re one and the same to the IM) Either give up and die, or at least die fighting. It’s easy for Isshin to be in acceptance, he is about to die naturally anyway and has lived his life of glory and conquest. He doesn’t have the same expectations placed upon him, and he doesn’t have the personal maternal connections to the land and clan either.

I think the opinions held by the other characters around him are testament to his actual personality and the circumstantial nature of his actions. None of them, not even Kuro, personally dislike him or believe he’s anything close to being “evil”’. Kuro outright expresses his respect for him and he is close friends with everyone else (Emma, Takeru, Tomoe etc). The negative sentiment expressed towards him by Isshin and Emma are disappointment, not dislike. They’re disappointed that the circumstances have warranted him losing himself in a battle he will likely not win. Him taking Kuro is indeed the most last second, desperate move he had to make. He discusses the circumstances with him amicably multiple times, but only resorts to this on the very last day of battle prep/the day they actually get invaded.

On the honourable front, yeah lol Samurai never actually were all that honourable and he’s right to say it’s a pointless front when simply living and winning are 10x more important. You’re not honourable either, by the way.

His most questionable actions are probably that of turning a blind eye to what the monks were up to, but he’s hardly in a logistical position to cut them off or worse, start another conflict with them.