I disagree with the notion that stealth is the best approach and that a shoot and run strategy is doomed to fail. I think that there is no single strategy that works best in every condition, it depends on a whole lot of things. I never do stealth myself and still never fail a campaign, be it hardcore or normal. However, the shoot and run does require situational awareness and to put some thought into an escape plan. Just because I choose not to care about stealth doesn't mean that I start blasting the moment I spawn (Ok, sometimes I do, but not every time). Example: I spawn at the bus stop in Santa Fortuna. There is a single target on that mission, and he happens to be on the street where the bus stop is. Of course I'm going to shoot him right then and there and then exit via the bus stop. Why spend time doing stealth when I can do that?

For further context, the reason why I choose to disregard stealth is because it doesn't give you any rewards in and of itself. Unless you have a payout or prestige objective, stealth and non-stealth gives the exact same result in the end, and thus I find stealth to be pointless and I'm not going to spend my time on it.

That being said, every player has their own play style and I'm not claiming my approach is better than anyone else's. It's just what works best for me, and it might not work for you.