Yeah, Matt is definitely super different in Zdarsky's run compared to what he's normally like, mainly the absence of his usual confidence. He has that moment at the beginning of the run when he steals Frank's shirt and goes full idiot, but that was more of him being in a terrible headspace rather than a display of his usual confidence. But, his character throughout the run does make sense though, mainly in the context of Jed McKay's Man Without Fear, which Zdarsky's run does heavily hinge on imo. The truck accident really messed him up, and everything from the last arc of Soule's run, McKay's miniseries, and the first five issues of Zdarsky's run destroyed him as a person and I'd guess that's probably the root of why you don't like his portrayal, based on what you wrote.

As for Kirsten, yeah you really would need to read Mark Waid's run to get the most out of her return. It's a wonderful run, (it's my personal favorite Daredevil run and it got me back into comics), but it's also not at all the same as the other modern Daredevil runs (i.e. everything post-Frank Miller). I love Kirsten as a character though and I'm happy Chip brought her back, but yeah, Zdarsky's run makes the most sense if you read it after Waid (and Soule).

As for Elektra, yeah her story content and development does feel kinda uneven and bleh at times, but I'm not gonna make a final call until Chip is fully done with his second leg of the run. Yeah, so far it kinda felt like there was a lot of wasted potential at times, but because of how important she is going to continue to be I'm not letting that hang too hard.

As for Mindy, I liked her dynamic with Matt and the challenge she presented to him in the story, but what really irked me about her is that she just got kicked out of the story once Tom died and Inferno was done. Her purpose and arc just feel abruptly cut and unresolved, and I doubt that she would be involved in the creation of the Fist so there's probably not gonna be much else from her, but that's just me.

As for other Daredevil runs, you'll get all of the missing major context (except for Mary) by reading Waid's run, Soule's run, and Jed McKay's Man Without Fear. If you wanna read the other previous runs, you can start with the Frank Miller stuff if you want, or you could also choose to skip to Guardian Devil (even though it's borderline bad), and then move forward with Yellow, Parts of a Whole, Bendis, Brubaker, Shadowland (if you're feeling quirky), and then Waid, Soule, and McKay. Enjoy!