Uh. No. TCP is complex because it works in the scenario where you, me, and 20 coworkers share a fast LAN hooked up to a slow pipe to the Internet and we all have to share that pipe constantly but nobody actually knows exactly who's trying to do what with it. TCP congestion control is a minor miracle even before you realize that this plays out writ large across the whole Internet, large-pipe-huge-pipe-small-pipe-big-pipe, without the Internet collapsing, which is what it used to do. One of the big challenges in designing fast scalable transports that gain speed by allowing drops or out of order delivery is in making them compatible with the congestion control regime that TCP implements.
TCP is complex because it solves a mindbogglingly complex problem. That it is as small as it actually is makes it one of the more elegant things ever to come out of computer networking.
> One of the big challenges in designing fast scalable transports that gain speed by allowing drops or out of order delivery is in making them compatible with the congestion control regime that TCP implements.
I would argue that this very thing makes TCP inelegant; congestion-control should really have been its own layer between IP and TCP, instead of being something that every protocol that's not UDP has to carefully reimplement.
TCP is complex because it solves a mindbogglingly complex problem. That it is as small as it actually is makes it one of the more elegant things ever to come out of computer networking.