The biggest arguments for drafting Carlsson were that he'd be more likely to stick at C which is a more valuable position, and his vision/game sense is very high. I think overall both will be very good players, just of very different types.
My original opinion was that Fantilli fit a bigger need since we were stacked at center, and having a top-line player that is actually a pure shooter would be a better fit overall. Since that draft, I've grown a lot more tepid on our center depth. Neither Zegras nor McTavish have really separated themselves, and as more time goes on I'd peg them more as 2C/3C tweeners than truly elite talent. So having Carlsson with 1C potential is now pretty important for the future of our franchise.