No, what's mad is that people actually think this.
Selling an academy player for £50M frees up... £50M. Not £250M.
You're thinking because transfers-in can be amortized over 5 years, the amortized cost will only be £50m. That's correct, but selling Garnacho only boosts revenues in the current year. With your strategy, we'll have £50M in extra costs in 2029 and 2030, but no extra increase in revenue. So we'll have to cut costs by £50M in order to comply with PSR.
A pound is a pound for PSR. It is a widespread myth that somehow selling academy players is this golden goose. Short-sighted clubs (hopefully not us) can use it to temporarily boost spending, but at the end of the day you have to account for all your costs.