Can only 50% of your surplus go to muscle gain even at +250?

Of course you'll never convert everything to muscle but I thought that training hard and keeping the surplus at around +250 could get you maybe 80/20 muscle to fat. But I recently read about the "p ratio" that says only elite genetics can achieve that; the vast majority of us can only hope for 50/50 muscle to fat conversion at best.

Anyone know about this? If true it might mean +250 is on the thin side.

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