Stealth length in single player.

I've started playing this. Looks great etc, but there are two problems.

1. How are you supposed to play this game? Are you meant to stealth most of it because I can't seen any other way being remotely viable.

2. If the answer to 1 is 'yes' then why does the stealth mode drain so quickly? It drains so quickly that it's almost unviable to use. You certainly can't run in stealth mode because it empties in seconds. Does the difficulty change how quickly stealth drains because I'm playing on veteran and it's frankly a non-stop death fest with loads of complete trial-and-error with trying to move between cover and wait for the suit to recharge. It's not much fun playing it like this with insta-drain stealth.