The real question is:
"When a player is DC'ing, what should they do?"
Constant DC'ing is one thing, but that random bug that boots you from a game and then you reconnect... what do you do?
If you're reconnecting at the start of a game, you play safe, farm safe, play catchup. (Within the first minute or two.)
If it's a long DC, the player has a few options:
Proxy-farm/push. Not the best, but allows them to potentially keep a lane pushed so your team can focus elsewhere.
If they have heavy CC, they need to be using that to disable enemies in teamfights. An Amumu ultimate may not do a lot, but it definitely can stop enemies and give the edge in a proper teamfight.
And the final option. Stick with the carry. Be the sacrifice, be the second support, do anything and everything you can to keep that player alive. Buy a couple wards, keep yourself between the carry and skillshots that can hit them. CC enemies who get too close if you have it. ANYTHING AND EVERYTHING.
It won't stop a total loss every time, but it at least can turn around a less fun game and maybe you will get that turnaround game or maybe you'll just make your allies enjoy themselves despite a loss.
But no matter what, yeah, there isn't any reason to complain or bash a player for what you can't affect. You can only post-game report and if the player is continuously reported for Leaving/DC'ing, then maybe they shouldn't be playing and deserve a ban that keeps them from ruining games via those DCs. A player should know what their computer and internet are capable of before they start a real game by testing in the practice tool or bots if nothing else. A player is responsible for playing their part in the match, that's the unwritten contract of hitting that "play" button.