Personally, I think Ramboing is viable, but you'll realize that stealth is more fun and rewarding. More to the point, it's not even hard, or at least, it gets progressively easier. This holds true for just about every single MGS game. I remember the first time I played Snake Eater (yeah, I am bringing this up for the millionth time), I was scared shitless. Some of you might remember the first encounter with enemy soldiers around the hanging bridge... and I had no clue on how to progress and was just hiding out in the bushes, scared out of my mind to be seen. The thing is, in older MGS games, you always had that shiny radar sitting at the top corner of your screen, with the eye-sight cones, telling exactly where the enemy combatants were looking and how far their reach extended. Easy. MGS3 - Snake Eater? Nuh-uh. Nothing. So the whole concept of how to do stealth changed with that.
Long story short, it took a while to figure out the quirks and the limitations of the game, or that of the enemy combatants. In time, you'll know exactly how to do CQC (Close-Quarter-Combat) and how to do it effectively. You'll learn and become comfortable on how to approach enemies when they are not facing in your direction, how fast you can walk or approach them without them noticing, or how they react when you throw your empty ammo cartridges near by to gain their attention. The game has a fine tolerance on what goes and what doesn't - and half of the fun in learning the game is learning exactly that.
MGS5 is no exception - and it gives you lots of tools at your disposal to make it even more easy. For instance, one of the most powerful tools you start out with and is a must, regardless if you're playing Rambo style or not, is your binoculars. Use it to scope out enemy camps and you'll see, enemies are marked automatically and then tracked, even when you are not looking through your binoculars. This is essential because you'll know at any time where the marked soldiers moved off too when you are infiltrating. In time, the binoculars is substituted to a degree by buddies you can take with you in the field who do the marking for you. Crawling around is also always a good and preferable method (in close proximity of enemies), at least until you figure out the tolerance levels of the enemy combatants and how well they see or notice things. And listen to what happens around you. You'll hear when enemy soldiers that you put to sleep or killed get spotted and draw attention. This either gives you a small time frame to put them down as well before they go into alert phase, or enough time to get the hell out of that area.
MGS is not a game that is meant to be played like an action game. As I noted above in my lengthy post(s), it just ain't rewarding, quickly loses appeal and is far too simple and to an extent easy. It's meant to be played stealth and when you do, the experience is very rewarding and there's lots of details and nuances packed into this style of gameplay that is otherwise completely missed. You know how you can play with a cat with a simple string and keep it entertained? MGS5 is just like it - it rewards and encourages you to play with the enemy combatants. Luring, tricking, sneaking, it's all there to be used and experienced. And as you learn the game, the game evolves with you, becoming more tricky by for instance camps being protected by cameras, higher level combatants with extra armor, helmets, night sights, or air support, hovering around the air, ready to step in when you're spotted. Play the game Rambo, and those details and gameplay mechanics are missed and lost and you'll find it isn't a very good 'action game' - because it was never intended to be one.
So, best advice: Play the game (yes, it's worth every single penny) and when you do, picture yourself as the Boss, lone soldier out in the field, all alone, on a mission to infiltrate. Don't get spotted, think strategically and learn the game. I suppose when you're new to MGS, it can be a lot to take in at first (like when I first played Snake-Eater), but stick with it and you'll have a very rewarding experience playing it.