It could actually work in a way to have them meet.
As Vader also says “You should not have come back.” So perhaps they did meet during the time gap and it also gives us a chance to see verbally “Obi-Wan once thought as you do.” Instead of it being expressed through Obi-Wan’s defensive lightsaber fighting on Mustafar. Plus how does Obi-Wan know he’s “more machine than man”?
There a couple of ways to work around it if they want to go that way.