Personally I always beat on myself for not putting enough detail in my panels, or not having enough backgrounds, and then look at other popular webcomics on the site and realise I frequently use more detail and more detailed and painstakingly created backgrounds than a lot of them do. 
Really, I know I'm being unfair to myself. The money in comics just isn't good enough nowadays to justify trying to prove something by eating into your earnings or health to put in more detail than most of the audience will even spend the time to appreciate. Most of them are reading on their phones in their lunch break or whatever, it's really only worth it if putting in extra detail makes you happy personally. Publishers will always take advantage of creators' urge to spend a bit more time than they're being paid for to make it a bit more detailed and finished out of a sense of artistic pride, and knowing when to stand firm and to be like "no. It looks fine, it's 5pm, pencils down and go make dinner." can be a skill in itself!
I tend to think of the level of detail that's "necessary" as "enough to be clear about who is in a place, what they're doing and how they're feeling", and ideally I want the place to be specific-feeling. I'm already putting in enough extra work by setting my comic in a Northern English Industrial city the characters are constantly moving around rather than somewhere generic I can just drop in premade 3D models of or reuse backgrounds a lot.
Some people tend to think of stubbornly sticking to making a more complex comic as a point of pride, but for me it's kind of something I consider an annoying habit; I should really have just set my story in a simpler setting it was easier to get reference for, and I don't know why I keep including stuff I hate drawing like cars... but I had a story I really wanted to tell and I have to pick my battles.
A lot of the time, I'll set up with a nicely drawn establishing shot when people arrive in a place, and then use as little background as I can get away with for the rest of the scene, or only use backgrounds when they're relevant to the positioning of the characters and similar. I also worked out early on that full shading wasn't going to fly. Here's an early inking and colouring test for Errant:
And yeah... it's kind of cool, but you can see I didn't even finish it. I was like "...there's no way I can make a comic like this and make two pages a week while having a job. No way."
So in the actual comic, it looked like this:
Pretty much only faces (and some very light coloured things on characters) are shaded in Errant, and mostly everything else leans on an edge highlight I can quickly throw on there. Yeah, it's less detailed than the above.... but what am I trying to do? Prove I'm a good artist who can spend a lot of time, or entertain an audience with consistent content they can enjoy on their phones? For me, it's the latter. I have nothing to prove, I know I'm a good artist, and that's what gives me the confidence to express things with simple lines and bold colours rather than hiding behind hours of complex rendering.
On a fundamental level, if the art looks finished, and it's detailed enough to read clearly, and has good variety of shots, and it's expressive and dynamic... it's probably fine! I think your example in that opening post looks fine. It compares well with the level of detail in plenty of popular comics, the poses in some ways read more clearly in the less detailed panel too.
