You might as well argue Brunel
...was a failure because his broad gauge was eventually reduced.
Brunel, like all engineers working at the bleeding edge, had many, many failures in his lifetime, and his vision could not only be strangely limited, but tunneled to the nth degree.
The broad gauge issue is a case in point.
Brunel's broad gauge had many advantages, chief of which was a much smoother ride than the standard gauge railways of the day, but it was more expensive to build and maintain than standard gauge railways were and could not be integrated smoothly into the national rail network, already established and growing apace and almost universally standard gauge.
For a man who understood so much, his attitude to broad gauge and the huge national public stink the "break in gauge" issue generated is a genuine puzzlement. Money was poured into the broad gauge rail system even when it was obvious to everyone that it could not survive.
Another gotcha in the GWR that should have been obvious as Bad Design from the get-go: a semaphore signal protocol that declared that horizontal means caution (or stop) and pointing downward means go. Everyone else realized that in the event of a broken actuator, gravity would be working in the cause of rail safety. Brunel's design called for counterweights to be added to make it all work the same way. More expensive, more complex, less failsafe (because there's ways the weights can fail too).
Brunel was a great man, but he was wrong a lot.
And the Broad Gauge was a gorgeous, magnificent, inspiring failure.
And I say this as a lifelong fan of God's Wonderful Railway and the people who built it.