I prefer the Ultimate Phantom Pain mod to Infinite Heaven, as it gives you control over the value of camo. I'm playing with guard sight x3, so increasing camo effectiveness to 600-800% is a necessity for realism.
Another great feature of UPPM is it contains a quicksave feature. It doesn't work perfectly as it's an experimental feature, but still invaluable for any stealth game. Its omission in the vanilla version is unforgivable. Getting good at stealth is about trial and error, why pretend it isn't?
I found that with the correct setup MG5PP is a stealth wet dream come true.
The biggest problem, in my opinion, that this game has (from a stealth perspective) is the lack of feedback and information gathering systems and tools.
You never know how visible you are, how various factors like distance, stance, time of day, camouflage, terrain, vegetation, affect your visibility, it's all just a guessing game. Apparently the guide offers some values for each of these but if you watch tests recorded on YouTube they don't seem to hold up. Basically nobody knows with absolute clarity and with contradicting information and lack of mechanical transparency it's just one big coin toss.
About trial and error, yeah, they kinda are. However, simple things like the drone and sticky cameras in Splinter Cell Blacklist, the owl in Far Cry Primal, the scouting orb in Thief 2, the disguises in Hitman, the cameras and drones in Watch Dogs etc. allow you to gather information without exposing yourself. With that information you can plan better. And execute that plan perfectly. This whole process takes more time than usual but it severely cuts down the trial and error and by consequence, save scumming. Phantom Pain has no feedback system and no information gathering tools.
In Thief the sound propagation system allows you to tell whether there are NPCs in your immediate vicinity, their general direction, how close are they relative to you, what surface they're walking on. That's a well made feedback system. And that's just the sound aspect of the game. You also have a visibility gem supporting multiple states, not the binary crap in modern games.
I haven't played the previous MGS games but from what I've read they had a camouflage index, basically a light gem equivalent. Why did they remove that in Phantom Pain? Anyway whatever. It's a good game regardless and it also has elements of immersive sims so at least that's something.