There's a motif in your posts that you might want to reflect on. I'll highlight where I saw it:
"I'm also very aware that I'm obviously as flawed as the next person (or more so!)"
"power imbalance is an issue in our relationship for lots of reasons... he is just so much more sure of himself about everything than I am. He is very confident he's right the vast majority of the time, and for a long time I think believed that but at the same time harboured resentment without really being able to pin down why."
"DH often has quite confrontational relationships with people at work (and two of his siblings often do as well) and understanding all that better would be really beneficial. So, if I can convince him that it'd be useful, I think it could potentially make his whole life a lot happier."
"he has had a bigger say in decision-making, which I have allowed/enabled because he earns more and therefore it seemed ‘fair’."
"he really struggles to accept things not being done the way he thinks they should be done and I am terrible at sticking to rigid plans"
What I see here is that you are very self-effacing, apologetic, even ashamed for being you. It's probably partly from having ADHD - I know ADHD associates with terrible self-esteem and a sense of inadequacy because you grow up feeling like everyone else got the memo and you didn't. But your H also probably consolidates those feelings rather than appreciating you for who you are. It's probably not intentional, and likely strongly coded by his autism (as well as patriarchy - double whammy). But I am definitely getting the feeling that he doesn't "see" you and he feels superior to you. In fact, I suspect he probably needs to feel superior to you. That need to be superior to others is likely why he gets into clashes at work as well.
This is not an equal relationship, has likely never been an equal relationship. You're being chonically exposed to a low level thrum of disrespect and neglect. That's why you're not happy in your marriage and feel resentment.
So there are two issues here:
(1) You: you lack self-esteem. And you lack a proper awareness of how much you bring to the marriage and family, as witnessed by the fact that you think that because H makes more money than you, you are automatically the less important person in the relationship. Frankly, you likely play a much much MORE vital role than your H in the family. He just makes money; you are likely the foundation of the family and the glue that holds everything together. You've got to work on both of these things in IC. He needs to be put in his place, he thinks way too much of himself. But to put him in his place, you need to be able to authoritatively step up to YOUR rightful place, which is right there NEXT to him, not behind him.
(2) Him: he is arrogant, self-absorbed, has little or no empathy. He has autism. He is also in his late 40s/early 50s? Imv, the chance of him changing meaningfully is small. You can try to point him in the right direction - "if I can convince him that it'd be useful" - but that's ALL you can do and you need to put limits on these efforts. It is very common for women to think, "There MUST be a way to get through to him, maybe if I say it this way, or show him, or write him letters." The fact is, there is no magic word or approach: he likely will not understand, either because he doesn't WANT to or because he is so emotionally stunted that he CAN'T. Women flog themselves to death trying to effect change in their male partners, but it doesn't work because you can't change others, only yourself. I have certainly learned that, to my cost. I often think of the saying,
"Men think women will never leave. Women think men will change. Both are wrong."
So, I suggest that you propose MC but also do IC for yourself whether he does or doesn't accept MC. It is possible that you standing up to take your rightful place in the marriage will improve things, make things more bearable for you. But it is also possible that he will resist this very strongly, because it might be fundamentally important to his self-esteem that you believe he is superior to you.
Btw, in relation to you having ADHD and him autism, there is a long-running thread on MN called "Married to someone with Asperger’s/ASD/ND: support thread". It is painful to read for me, because some of the male partners are so egregious and the posters (many are ND themselves) struggle so much to leave, but it may be helpful for you.
https://www.mumsnet.com/talk/relationships/5447569-married-to-someone-with-aspergersasdnd-support-thread-17