I can't help but think about all the non-web3 protocols this applies to, like email, html, etc. It's slower, but it's more powerful. While Signal could implement video chat any time, true...we don't need another closed video chat.
Also Signal is open source, unless you have a different meaning of “closed video chat.”
uniswap is a good example. when they release an upgrade users must explicitly adopt the new version. in fact uniswap v1 and v2 still see usage despite the release of uniswap v3.