The maxim "every tuneable parameter is a design weakness" applies for top-down design, but not so much for something as foundational as the IP layer. In the 70

The maxim "every tuneable parameter is a design weakness" applies for top-down design, but not so much for something as foundational as the IP layer. In the 70s, TCP's inventors imbued it with solid fundamentals, but could not have anticipated how the protocol would need to evolve in the future w.r.t. security and performance. For IPv6, there are unknowns that will only encountered at scale, and implementors are hugely motivated to play fast and loose with the spec. (TCP Fast Open converts!) Bottom-up systems have inherent wiggle room, and shipping them with sensible defaults is only possible in the short term. That's not to say we should design over-complicated systems, but just that fine tuners are not a weakness.