There are a couple of true points here, but Ronaldo was on a totally different level at the age of 16 and far more important to his teams than Rashford is and probably ever will be. Ronaldo went to Real Madrid at the age of 24 and immediately turned into the one guy on the pitch who decided games just by himself. Now think about what would happen when Rashford went to Real Madrid. There is no chance he would ever get close to what Ronaldo has done as Ronaldo is several categories above Rashford.
Sure, not everything about Rashford and Ronaldo are the same. I don't deny that Ronaldo has a much better career at the same age, Ronaldo even already become a superstar player at 26. However, Rashford career at Man United isn't very bad, he was predicted as one of the most potential players. Sadly, Man United never hired the right coach, so Rashford can't optimize his potential. It was different with Ronaldo, he was under Ferguson's management at that time. It was one of the factor that Ronaldo can easily become a star player. If Ronaldo has the same experience as Rashford, Ronaldo may never be a star player.
Don't forget that I am not the biggest fan of Ronaldo because of his bad character, but his performances as a football player are not up for debate. Even when someone didn't like him, nobody could ever deny that he was one of the craziest goal machines football has ever seen. 2010/2011 was the first season he scored 40 goals in La Liga only, that was at the age 25/26. Rashford wouldn't have the potential to score such a number of goals in La Liga. Rashford's performances are far too erratic. Sometimes I like to watch him play as he is delivering with his speed and great technique, but then there are days where you have to first check more closely whether he is even playing.
We are not debating about the character of the players. We are just discussing some matters about Rashford and Ronaldo. I think Rashford has the potential like Ronaldo although he may never be like Ronaldo. Sure, Ronaldo could score many goals in his career because he was supported by many great players and was managed by brilliant coaches. Meanwhile Rashford has a different situation, he is growing in Man United when Man United is in a crisis. If you consider the condition of Man United, you must understand why Rashford's performance is still erratic.