I also agree with the issue you mentionned.
We felt the long area of play was important in early waves so player can get the hang of it, and in latter waves so they have enough time to defeat more monsters.
Still waiting for that first goblin when restarting the game can be frustrating, maybe adding a x2/x5 time speed up button would help solve the issue.
Again, thanks for taking the time to explain further, we, as a team, greatly apreciate it!