These are actually really good drawings, if not traced. You didnt post a link to the tutorial so i cannot compare but i do think you could focus on drawing more feet, hands and faces as those seem to look a bit off in the drawings. Continuing to practice and really looking at the differences between your drawing and your reference will help you find the small details/mistakes you missed.
I really like the shading you did on some of the figures, it really brings out their volume.
I think youre being very harsh on yourself, 30 seconds isnt a lot, i feel like youre trying to do the whole drawing in 30 seconds when you dont have a clear grasp of how the human body is generally constructed. 30 second sketches are very much for capturing the bare essence of a pose rather than the musculature (especially if you arent very experienced), if you want to capture more i reccomend increasing the time to 60 seconds for your "quick drawings" and also doing longer drawings to try to get the details right. Drawing individual body parts outside of practice (you can go find images on medical diagrams and sites like Pexels or youtube videos), learning certain rule of thumbs when it comes to the overall body proportions and measuring with a pencil on your longer drawings can go a long way! Just keep at it!
Another piece of advice, completely optional but it might be worth trying to draw with pencil on paper, it might give you more fluidity and confidence compared to the digital medium, especially since the undo button isnt available. Also it is easier to get into the workflow since you dont have to paste the image to your program and then start drawing, personally this helped me a lot to draw and to stay consistent!
