If Merlin cans see the future, then why did he choose Arthur? Isn’t there someone else more worthy? Or are Merlin’s future seeing abilities as sketchy as Rumples seer?
I think Arthur is worthy, he just became obsessed about the wrong thing. All that dedication and hard work and myopic effort to finding the missing piece of Excalibur could have gone toward healing the kingdom. It would have been a success. He truly could have been a very good king. But, like so many other villains, he got distracted by shiny shiny things and focused on the wrong endeavor. So, it’s not that Merlin was lying or wrong or that his powers aren’t up to snuff, it’s that Arthur made a choice, largely based on Arthur’s own understanding of the prophecy and what it entailed (he must have the sword and he must have Guinevere). If he does not have those, then he can’t be the King.