1. Since DM goes to 40 kills, the absolute maximum of time wasted in death delays could be 40*3 seconds = 2 minutes if someone actually died 40 times. I can't pull up my stats now, but 20 should be close to or slightly higher than average amount of deaths in DM. Thus, average amount of time wasted per game is about 1 minute.
2. Of course there has to be a good reason to justify wasting all this time, but finding any meaningful reason for this is extremely hard. Delay is a punishment for death. Obviously, it can only come from a mindset that DM is a mode people should try to win as opposed to viewing it solely as warm-up and training routine. Already a dubious goal to sacrifice everyone's time for. But what does it achieve? To a small degree it encourages people to play more cautiously. It also makes camping a viable strategy... The only silver lining I can think of is that being more cautious could lead to building less bad habits. That is, if 3 seconds would make you more cautious, which I highly doubt. It's noticeable in the grand scheme of things, but in the moment you only see it as a small, but annoying inconvenience, not something that would affect your strategy.

P.S. I haven't checked the new patch that's probably already live, but it probably doesn't change this situation. This is a repost of 15 days old post deleted by some moderation filter.