This is why people think Little Mac sucks. Little Mac has an absolutely dominating neutral. If you truly believe that Rosalina beats Mac in neutral, you're either crazy or don't understand the matchup all that well. Little Mac keeps Luma dead the whole match. Once that's done, his frame data is so much better and his smashes have super armor, allowing him to win just about every close encounter. With the new shield mechanics, Little Mac is basically unpunishable on many moves. What do you do against a Little Mac who perfect pivots in and Uptilts? D-tilt? His U-tilt beats out our D-tilt and there's no way you're going to block and punish either.
But of course: "All you have to do is throw him offstage then hit him!!!". The only issue with this is that we die at 50% to a super armored F-smash... and when Little Mac inevitably wins neutral and we're offstage, he's going to D-smash at the ledge and we're going to die because good Little Mac's are consistent with taking advantage of ledge vulnerability. (Same goes with Ike players and eruption. You're never getting back to the stage free against them). So in reality, who actually is going to die more easily? Another key thing worth mentioning is that this is one of Little Mac's easiest matchups in the game...