In my opinion, making a game accessible to all players as much as possible is more important than competitive statistics. When players are experiencing disconnection issues that prevent them from finishing a game, they are likely to become frustrated and potentially quit the server. If someone disconnects and gets a death added to their stats, they probably won’t even notice, and I doubt they would quit the server over such a small thing.
Not implementing this because not everyone could join back within a certain amount of time is a bad reason to not implement it at all. It would be better if at least some players could join back, and we shouldn’t prevent them from rejoining just because a few players aren’t able to. I think that the majority of players would be able to join back within a reasonable amount of time.
I also think it is a bad idea to not implement this because of speedrunners. Intentionally preventing players from rejoining their game just so speedrunners can rely on disconnects to achieve faster times seems like the incorrect thing to prioritize, and doesn’t sound like a fun or accessible meta for speedrunners either. This would favor players who are less prone to disconnections, giving them a competitive advantage over speedrunners who are more susceptible to these disconnects, so I think implementing this would make speedrunning more accessible if anything.