I was in trying to compose a longer reply yesterday but had to pay attention to my day job, so I stopped.
Here's the thing.
ScubaBoard is different. Less than 1% of divers participate here and overall it is an elite segment of recreational diving as a whole. It is made up of doctors., instructors, cave divers, captains, industry pioneers and leaders, and other people who write in complete sentences and care deeply about diving.
Outside of ScubaBoard, diving isn't like that. It is an activity that cuts across class lines and, to a considerable degree, demographic groups. The majority of dives are conducted by beginners who have no intention of ever becoming the fully autonomous, streamlined diver with perfect trim and buoyancy that is the ScubaBoard shibboleth. The majority of instructors, in my experience, do not take streamlining seriously and see buoyancy control as an advanced skill that students will learn after completing their OWD class.
You, Marie, are one of the 1%. Your eyes have been opened. You notice things that other divers miss or consider unimportant. The only trouble is that you don't yet realize that you're part of the 1% and that the things you see around you are
typical: Larger classes, instructors who have to choose their battles, students who do not pursue excellence, poorly chosen gear, and an enormous amount of bumbling around. You can't change them, of course, and it's not your responsibility to try. For me, the "aha" moment came when I took my AOW class and then came here and wrote a post with remarkable similarity to your opening post in this thread. So, congratulations, you've arrived.
Now what? Go out there and, to paraphrase a variously-attributed trope, be the change you seek in the world. Have fantastic trim, buoyancy, and streamlining. Tell your friends about the fun times you have diving. Pursue excellence, and be a quiet positive example to those around you.
And that class you saw? They probably did fine. One or two of them will muddle through and go on to become pretty good divers eventually. One or two will realize the diving isn't really for them. Sadly, one or two that could have been helped by really excellent instruction will probably give up. C'est la vie. A fact to consider is that the instructor and DM probably saw much of what you did. Most (nearly all) are very good at watching their students and catching problems before they snowball.
And that is the world we live in.