Mystery Solver #1
You'll have no doubt read about the prototype sheet describing how Tails was GOING to be added to the show. He would be a 2 year old toddler-fox with a very deep man's voice that acted like a cowboy and talked with a big funny drawl like a cow-poke. Because that's somehow appropriate. /sarcasm
Everyone always remakred about how that made LITERALLY NO SENSE AT ALL
And there was no context nor reason to have him be like that, until you see these sketches here that explains it. Look at all the "Western & Riding" stuff that's all over him. He's almost always got spurs and cowboy boots, there's literally "Riding Crop" notes and horseman's boots. Somebody really, really wanted this show to have western elements in it and they were going to get them however they could. If Robotnic couldn't be a cow-poke-pig, then they'd have their Cowboy Tails instead. Fortunately though, the weirdo-western elements were all taken out of it.
Mystery Adder #1
Why the hell western and who was behind it?

Sketch Talk:
Knowing about animation/background can give you gimmick ideas that would be here, like the "Bird Neck Ratchets Out", the sparking ponytail, and probably opportunities for the spurs to spin like buzz-saws or his body to have lights on it to 'do things' in the show. He had the riding crop to hit things when he gets mad (Turned into fist slam in the show) He's gimmick loaded on purpose, which is good character design/you want them to be entertaining to watch so it is good to see this sort of thing being taken into consideration.

The top right/full color:
This actually did get released in a promotional ad/page.
"Robotic Doctor"-
Here he is with mace-cluck again, but both arms are robotic and the upper sleeve is chainmail. The wizard cape is now a coat, and he has "Mad Sceintiest" wire curly crazy hair on the sides of his head to make 'more mad science'.
"Robotic Sneakers"
All his limbs are robotic this time, and Cluck is looking aggressive. The big "R" on the shirt looks very Team Rocket from Pokemon. The coat has too many buttons to be practical for western animation. The head retains Frankenstein with stitches, neck bolts, tall head and 5oclock shadow/big jaw.
Both walking away & front facing it's the same design. You can see the Frankenstein toning down & the Western Cowoby rising. The face is pig and gorilla combined, with a metal mowhawk.
"Far Right White/Blue Sketches"
These, of course, are closest to how he ended up. Especially the bottom one. See them checking off the 'high tech boot' shoes, how he kept the cape the entire time, and lost all the Frankenstein , pig & gorilla elements

Why No Eggman?
Why Re-Design?
Look at all this work going into making a character that was already created. Dr. Eggman, of course, already existed.
So we know half the re-design is to fit him into the Demon Wizard role that was the core of the original show.
The other half came from Sega calling him "Dr Robotnic" because "Eggman" was somehow "Too Wierd" for kids.
Uh-huh, a man named "Egg Man" was TOO WIERD when Plumbers went into a magic mushroom land through pipes to fight flying turtles because plumbers doing that is not wierd in any way. Uh-huh. (Remember: the Super Mario Super Show was well/year before this one yet---here we are)

The "Robot-nic" aspect escaping them?
Yea kinda seemed to, both this and Adventures of Sonic also couldn't decide him between "fat oaf stupid" and "robot-maker man smart" villain (one more than the other, clearly) Pig-gorilla-Frankenstein the cowboy never came across as 'dangerous genius'.

Actual Eggman:
He's neat because it's not necisarily HIM that is scary, it's what he MAKES that is scary. He's not monsterous, but what he does, is. That could have been something rad to run with for a show, but no 'eggman' is too wierd of a name & a character to look at but Pig-Gorilla-Frankenstein-Cowboy sure is acceptable in his stead.