FWIW, I can very much relate to that. If Discord had no web client (i.e., if installing a client was mandatory), I probably wouldn’t be on it. I do not think it is reasonable to expect people to install proprietary software.
Lucky enough, there is a web client. Unlike Gitter it required some configuration (110% font zoom) for text to even be readable (not sure how that can happen with a chat app), and it shows annoying banners at the top advertising for Facebook (“connect your account”) and the XBox (“install the app”) after every login. Not great, but bearable.
The UI is also worse than Gitter, with private chat and group chats being split into two views and the group chat view listing two dozen channels of which I care about three. Whenever I open the Rust “server” on Discord I am greeted by 10 channels having new messages, so I just ignore all of them. Not sure if there is a way to permanently hide/leave individual channels, but I think the IRC/Gitter model of just joining the channels you care about makes much more sense.
So, overall, both in terms of freedom and in terms of user experience, I see Discord as a step backwards. I appreciate Gitter was unusably bad for others (I never had problems beyond mild annoyances), so please take this as just another data point.