Yay, Tomahawk and Centaur Men. I was thinking about doing a few robot masters, too, but we'll see how that goes.
Seeing as they're two years old, I really don't know what to tell you, but it appears by the way that they're drawn, it's mostly sketchy in the lineart. You probably weren't too concerned about absolute perfection, you just wanted to get the idea out, and I like that, honestly. Besides, the RMs only got more detailed in design anyway as the series progressed... and then dropped back down to being too simplistic in 9. That's some kind of regression right there.
Also, I'd prefer not to be an artist by career myself, but I admire how you're still willing to learn anyway. I feel like that's something we all ought to do, whether we're taking this professionally or not, mostly out of a sense of pride for our accomplishments. You'll get stuck in a rut otherwise, and it just won't be as fun anymore.