That’s a bit simplistic - a very short spawn time, like what we have now, reduces the effectiveness of spawnwaves as there are simply more ‘spawns’ for the dead to join. If you double the defense spawntime from 15s to 30s, then more players, on average, will spawn at the same time.
The problem with the OP and a lot of others is taking one bit of this game and suggesting a tweak, believing it won’t have a significant consequence elsewhere.
On the subject of other games with this, CS 1.6, CSS and CSGO all put you out of the game for the time remaining which can be well over a minute…

