I disagree Scooter.
Potentially we could sell him, sign 3 or 4 quality players and go up. Alternatively, we could sign 3 or 4 flops, while we watch Brooks become the next Walker or Jagielka.
Wilder's record in the transfer market has been impressive, so I'd have more faith in him spending the money well (unlike previous managers), but even Wilder has made mistakes so it's realistic to expect we'd inevitably waste a percentage of the sale.
We'd likely replace him with someone like Maddison, who is no more of a known quantity in this division than Brooks and doesn't have anywhere near the same potential.
And the point you make about Slew I feel is flawed. Great, we made £1m for selling a player before we got to see his true potential, and we won - he never got there. But what about Kyle Walker? We got around £2m for someone who was worth 10X that a couple of seasons later and 25X that today.
Brooks may never make it to that level, but if he does, it would be nice to say we got to see him for a few seasons and remember his contributions - Unlike walker, who we sold after a mere 5 appearances.