I always stack my teams heavily with closers. In my 12 team league I kept 2 closers out of 7 keepers and stacked up early with more good closers. I'm about to win that league second year in a row now with an 18 point league heading into this last month. Having a closer/RP heavy team has always worked for me. It almost guarantees you to win the SV, ERA, WHIP and helps with good K/IP, if you do a few smart streams throughout the season and have an ace to rely on, you have nailed down the pitching categories. and if you do mediocre in the batting categories you have won the league. Its all about loading up on those high strikeout RP's/closers, unless your league does not have alot of pitching slots.
Stacking up on closers will only guarantee you one thing, SV. If you don't have good enough SP because of your choice in closers, it won't matter how good your closers are, your ERA, and WHIP will suffer.