Couldn't help but think it should be the other way around. Both are extremely graphic without a doubt, but personally still think that Dead Space should be rated R18+.
Source:
RE4: https://www.playstation.com/en-au/games/resident-evil-4-rema…
DS: https://www.playstation.com/en-au/games/dead-space/
I think someone born in 1998 will be okay