This is debate between the second biggest godzilla's.

I say it a tie because they're both godzilla but it can go either way fo
them. Shin could win in long distance due to his fire power but we don't if he has any combat experience or if he gets any in the next movie or comic/Manga and his back is his weakness . Legendary wins in close combat due to his strength and durability and  may lack the beam but still can win. He took on two Muto and had a building fall on him but his gills are his weakness so shin could bit him but we don't know the battle would work. So in my opinion, I say a tie. Have a good day.