Everyone can improve and have the kind of channel that gets viewers, and be entertaining in some way. No, everyone can't be number one, however, that's not how everyone defines personal success. I'd keep improving. If I'm monotone I'll practice. If I'm bad at promotion I'll work on it. If my editing, branding, etc sucks I can improve with research and practice.
Another thing is the "doing YouTube for the right reason" which is complete and utter nonsense. Whatever reason someone decides to do YouTube it's the right reason for them. If there is one persistent theory on this board I'd happily beat to death with a baseball bat is the constant "right reason" dribble.
YouTube is just a website owned by Google used make tons of money from advertising. It's a business and nothing more. Bottom line. So if someone wants a little fame, go for it. If someone wants a little pocket change. Make it happen. If someone wants more, work your butt off and you may or may not get it but you won't have any regret.
Just like everything else in life. Results will reveal themselves but how are people going to know unless they try.
I would suggest never letting people anywhere talk you out of your dreams. Dream big, work hard, and adjust as you go.