not even deeply disappointing, just mundane old disappointing.
The Millenium prizes weren't about massive impressive computational achievements, and true to form this counterexample is actually useless for actual Navier-Stokes sims, provides zero efficiency gains, doesn't even preclude input ranges that anyone would actually use, etc.
The prizes were set at that level with the idea that the prize money was small enough to encourage individual mathematicians to engage with these problems, or encourage non-mathematicians to seriously engage with math. They were small enough that it was judged that larger corporations wouldn't engage with them because the problems themselves weren't really anything they could profit off directly without also contributing to their competitors.
It is typical of OpenAI's lack of strategic foresight that they'd tell people in the press release that they spent $20 million dollars for a $1 million dollar prize. They just wanted to tick a box, and again true to form they completely devalued the achievement in the process.