I know minecraft is a little heavy on the mob spawns these days but... is it supposed to be like this?

Johnnyboy got me thinking, precisely how many are there here? i just roughly counted, there are just over 100 hostile mobs in that screenshot.
Boy, I sure do love lag. Would be such a shame if somehow the mob spawn rate was decreased
Seriously though, is that possible? had some consistent lag the other day when there were just 4 people on. we suspected it may be due to the amount of mobs, barring any other server limitations, now I'm certain that was the cause.