For me and most of the people in a group that I game with here and there, Discord has been pretty painful through the time we've used it. We've had problems with voice cutting out, with it reading mics that are perfectly configured in windows and working elsewhere, and with it causing sound in games to cut out. I understand why people use it, it looks much more modern, its easier to learn how to use and manage, and anyone can create a server for it at any time. However, they still have a ways to go on it in my opinion before it will be anything completely dependable.
I'm not sure how much I agree that we are losing people because we don't have discord. Anyone that isn't involved enough in the community to download the teamspeak client and install it (a 5 minute process), more than likely isn't dedicated enough to bother joining a discord server we are in and then joining voice or even chat channels.
If we have both, we automatically lose admins and people in both, and split the population in two, in something that is intended to bring the population together, not split them apart.
I do however believe strongly in going the direction the community wants to go. If you think more people would join, then the real test is whether or not you can get them on here and vote. If they won't bother voting, they won't bother joining our discord if we had one.