You're cherry-picking an interpretation of a single sentence, when it should be read in the context of the preceding one: Ousterhout says every aspect of TCP's design is wrong for (modern) datacenter computing. He's not saying bad decisions were made at the time it was designed, nor even that it's badly designed for other use cases today.
The first few paragraphs of the article give even more context:
> The TCP transport protocol has proven to be phenomenally successful and adaptable. [...] It is an extraordinary engineering achievement to have designed a mechanism that could survive such radical changes in underlying technology.
> However, datacenter computing creates unprecedented challenges for TCP. [...] The datacenter environment, with millions of cores in close proximity and individual applications harnessing thousands of machines that interact on microsecond timescales, could not have been envisioned by the designers of TCP, and TCP does not perform well in this environment
The first few paragraphs of the article give even more context:
> The TCP transport protocol has proven to be phenomenally successful and adaptable. [...] It is an extraordinary engineering achievement to have designed a mechanism that could survive such radical changes in underlying technology.
> However, datacenter computing creates unprecedented challenges for TCP. [...] The datacenter environment, with millions of cores in close proximity and individual applications harnessing thousands of machines that interact on microsecond timescales, could not have been envisioned by the designers of TCP, and TCP does not perform well in this environment