The premise is wrong because

99.9999% of "clients" are way worse than any browser for same service

so just throwing such advice around is wildly irresponsible. Examples given were

alexandrite for desktop - does not exist and if it did it would be what, an electron app?

Gemini - impossible or unweildy to use web browser anyway. gemini is a revamped gopher. You can access gemini via a web proxy but i doubt that is substantially worse than using a client https://geminiprotocol.net/clients.html either a proxy or client could contain malicious or sloppy code

neon modem - a github project with 9 contributors https://github.com/mrusme/neonmodem. it is a TUI interface for an itty bitty nichy part of the web. Cool to find out there is a tui for lemmy i will try it because i am a total weirdo not a normal person. It took me years to learn enough to be able much less willing to try a tui for fun.

So we have zero examples. Better but still not great example would have been reddit with 3PA prior to the API changes. Or mail cient vs webmail. Or usenet vs forums. Or bittorrent streaming vs netflix. Ytdlp vs youtube. Rss vs most other options.

Web is universal and low barrier. If you want to move to clients for everything youd have to rework every kind of function done on the web. Personally i like using special FLOSS clients when i can (like the lemmy client i am using right now) but i dont want it for everything. And a lot of the coziness with volunteer small groups of devs would vanish with any degree of popularity. A lot of the vulnerabilities that persist are pervasive to the internet and need systemic solutions like net neutrality and enforcement of regulations. Same problems could easily reproduce themselves with the proposed solution. Security thru obscruity sux.