I gotta admit, I didn't expect this. I saw it initially and went, "Oh great, Marvel is making a Suicide Squad movie." I was pleasantly surprised to learn that this was not necessarily the case. Light spoilers ahead.
While the parallels are there on a surface level, I think what really makes this so much better than its DC counterparts is the motive for these characters. It's not, "Do this job or I kill you," it's, "We all have a common threat and similar backgrounds, so we can give each other enough grace to help one another overcome our obstacles." I think the idea of feeling unfulfilled and pouring yourself into work is universally relatable, so using that to humanize these admittedly D-list characters and make us actually care about them was clever.
The themes were serious. I think that the success of shows like The Boys really let Marvel (or more realistically Disney) see that more nuanced topics can be covered in this medium. In my opinion Iron Man 3 suffered from them avoiding touching on Tony's alcoholism from the comics, and that sums up a lot of the general cleaning up of these characters in the past. They're still fine movies, and they are more accessible to families that want to have their kids watch it and then buy action figures, but it does water down the characters from their source material. Letting them show that, yes, these people are actually affected by what they go through and not immediately writing that off with an ill-timed joke goes a long way to help the story. I think that trying to keep us hooked solely by increasing the spectacle of each villain will get boring VERY quickly, so having them finally take a step back and realizing that it's the relatable parts of these characters that we actually care about is refreshing.
I do think at times it was a little ham-fisted, but I think that's just inherent when discussing anything mental health related nowadays. It's difficult to make an interesting story about these topics while staying tasteful and not villainizing people with mental illnesses. However, this movie is a giant leap in the right direction compared to the last several projects Marvel has put out, so I consider it a slam dunk. :D