Pretty much agreeing here.

As pertains to illustration, the pendulum swings in a few different directions, but especially familiar to me is that between meticulous detail vs. fluid gesture. It's one thing to dig in on a single piece for a long time introducing layers of detail, it's quite another to find more thrill in the expression of form and body positioning. I certainly know I like the latter for my own part - Frankly it's just more fun to sketch gesture than dig in on details, and the more you do art *for you* the less appealing going cross eyed on details one gets.

I'd say you improved greatly. No need to be hard on yourself.

I've heard that improvement with art is a bit of a cycle. Whenever you feel you're plateauing or getting worse, its actually that your artistic eye getting better. With time and effort in improving your craft you'll be able to hit a good breakthrough and shake that feeling of stagnation!

I have a theory that while you're trying to figure things out you're going to be more experimental than when you've got a solid, practiced method, so you might be appreciating/missing the little ups and downs of your older world which don't pop up in your newer stuff. If that is the case, you can probably get that feeling back by experimenting more.

(Disclaimer: I'm not an artist or anything, but I thought it was worth saying anyway I'm case my solution helps)

Just gave things a quick comparison. I'm gonna echo some of the things others have said up here, it's likely just the self-critical mental trap resulting from an unfair comparison because of the increased amount of detail you used to put into things: for example, the thicker silhouette outlines and soft shading. As others said, making comics takes a LOT more time to do, and any shortcut you can take to cut down on production time while still looking decent is the way to go.

I'd say you have improved significantly, but just as a thought experiment to actually prove that to yourself and break this self-critical idea, a fairer comparison would be if you tried to draw something new in a way that imitates your older style. I think you'll find yourself correcting errors and employing advanced techniques along the way that prove you're far better than you used to be. Really feel out what you do along the production path and drill down into the details, and mentally compare what you're doing now to the way you used to do things. You'll understand exactly where your gaps in knowledge were back then, and how they have since been filled. That's the method I used to break myself of the mental trap of feeling like I've gotten worse instead of better.

No your art did improve and your are more critical with yourself
I saw that with many artists at the start they just draw and didn´t reflect anything but over time they got more and more critical with themself
your art got more dynamic and fluend which in my opinion is very good
Also you switched your style to that of an comic artist from an Pin Up artist and gave your characters more life and motion.

I dunno if its improved or not, but do remembee that youre your own worst critic.

When it comes to art, things get really, really subjective. So, instead of asking, "Why is my art worse now?" ask, "How has my art changed since then, and what desirable qualities from then are missing in my current art?" Not only is this a more mentally healthy way to approach the problem (it doesn't assume you're somehow lesser than you were before), but it also states the objective in the problem itself. That is, you want to recapture some qualities of your past art style.

Personally, I don't think your art is worse now than it was five or six years ago. It's different, but it's not worse.