Lots of people getting MGS V platinum.
You don't need the objectives to get an S rank. S rank are very easy since doing them fast rewards so many points and can do missions extremely fast if know what to do already. D-horse is actually best buddy for S rank due to the speed he provides.
Can do all objectives once unlocked stealth camo (which requires no skill to achieve and is just a R+D unlock), at which point really is no challenge at all.