If you're using a shotgun you're not strictly following a stealth build. If I only put points into gunslinger, archery, light armor, hidden strike, and from the shadows, I don't have any trouble. I'm annoyed by all those rooms that you run into that stealth doesn't really do you any good because you trigger the mob but if I can't use my crossbow to kill them, I mow them down with the 9 mm. Later on when I get the SMG and some of the books that back automatic fire up, I generally start a new game because things begin to get boring.
In the game I'm playing now I'm a little behind the stealth curve because I put some points into strength to get MasterChef up to two. I like to cook. I don't really need it. I also like clubbing zombies with a baseball bat. I find it a great stress reliever. So I have maybe 6 points not in the agility tree. Yet I'm doing just fine.