I don't like it either. How do I use the older version?
However, the user-agent spoofing works because it fakes IE11 on Windows 7 and it triggers a server-side override.
rweb_optin=off
dnt=1
and then navigating to https://twitter.com/i/directory then your user profile via the settings dropdown (next to [tweet]) seems to set you back to Legacy Twitter permanently without breaking your user agent.