Zerg units tend to specialize in killing a specific type of enemy, which is easily seen with so few units being able to attack both air and ground. This means we need to have constant scouting to make the right choices. This is where the meta-game starts hurting us. Terra players will often block the entrance to their base, and best early scouts are ground. Later in the game our stealth scouts will be detected by decent players as well, leaving us mostly blind. We can use a mutalisk to scout, but that requires us to build a tower and branch out from the specialization that is so necessary.
The other races don't have this same problem with scouting. They have units that are more versatile, and have better scouting (e.g. scan). Our lack of these things leads to Zerg being easy to counter. If your enemy prevents your scouting (which is not very difficult) then they can win via massing a versatile unit. To me, this is a much bigger issue than queens and spawning larva. You could have an unlimited number of larva, but with our unit composition we won't win without a better solution to scouting in current strategies.