Comment by skissane
What are those flaws? And are they inherent, or something that could be fixed with enhancements/revisions?
TCP as originally specified had fundamental design flaws too, but the TCP of today has significant differences from the 1981 TCP standard (not the first version of TCP, but the first version to see significant production use).
Off the top of my head: stream count is static (an extension exists nowadays, but it's still usually unsupported), startup requires requires excessive round trips, and it's unfixably insecure (TCP actually shares this last flaw - you can only detect, not discard, injected packets - and this causes massive reliability problems in the real world). Some of the default tools were also horribly flawed even by 1990s standards (e.g. a shell script which uses $* instead of $@) last I checked.
Certainly there are things that could be done to improve the ecosystem - but why bother when you can just use a reliability layer on top of UDP instead? And these days there's a "standard" solution so you don't even need to compare choices or worry about design flaws affecting just your program: just use QUIC, everybody uses it and if something goes wrong the world will scream and the shared library will be upgraded by the distro.