That was only true for the original Titan. By the time we made it to Pascal based Titan it was gaming only.
https://www.tomshardware.com/reviews/nvidia-titan-xp,5066-14.html
"Once upon a time, the Titan name represented prosumer-level functionality. In addition to great gaming performance, Nvidia’s original Titan boasted theoretical FP64 processing power on par with the company’s Quadro and Tesla cards via GK110. That changed from Maxwell onward, where double-precision fell to 1/32 the rate of peak FP32 performance. Half-precision in the Pascal generation is even worse: you get a 1/64 rate of FP16 compared to FP32."
RTX 2080 was faster on average at launch, it has pulled away even more with 2 years of driver developments. There no question which is faster. 2nd Titan X is closer, but still faster on average. AMD does not have a card faster than the Titan X, and won't within 4 years of that card's release. You're really grasping for straws here.