I've seen lots of skinny little dudes get very big with drugs. Definitely drugs are the single biggest factor in building muscle and strength. If one wants to win bodybuilding contests then genetics is important. Symmetry etc.
I don't agree that "drugs are the single biggest factor in building muscle and strength" Actually training and eating right/enough on a pro-longed and/or consistent basis are the biggest factor. You can take all the AAS you want, and nothings gonna change without training....not much will change without eating enough of the right stuff. I'm talking about looking good, not blowing up from Mickey D's...drugs will amplify growth, but the person will likely look like shit.
Now, if you said single biggest factor needed to turn/be a successful pro...yep, agreed.
The skinny dudes that are able to do what you stated, yeah that's closer to being "all drugs". They have something going on genetically that makes them hyper-responders that should be studied at some point. Look at Flex Wheeler as a kid......no one woulda thought that dude would be huge. Even still though, he had to train hard and eat right to become what he did in pro bbing.
As I got older, and newbies would come into the gym I worked at it was truly amazing to see some guys that had a good 2-5 years of training and good physiques all of the sudden turn into "holy shit" physiques in less than a year.
I've been around it along time, and that type of response is not the norm.