Totally agreed. TCP is a great general purpose protocol which has been working "fine" in all cases. If it doesn't work well in a particular situation, then I believe its our fault that we are trying to fit it there just because it works.

Here is an example of what a custom protocol built over UDP taking in consideration the very specific use case of mobile devices accessing wireless networks, could do to achieve better throughputs than TCP, details here:

https://packetzoom.com/blog/lessons-learned-tcp-slow-start-d...