I agree. I do think that IF you spend 2-3 years gathering all the young pitching you can get, then you should be open to trading older pitching (even if it's not really old), given the right return, unless you think that player is the rarest of all pitchers, a true ACE.
I look at it this way:
Who has more current value: Teheran OR Allard (change Allard with Touki or Fried or Soroka or Newcomb or Anderson....as you wish)?
The answer is easy. Today it is Teheran because he is a known commodity at the ML level while all the others are projections. So, at this moment in time Teheran is more valuable, no question.
But what about 2-3 years from now?
That answer is not known and is unknowable because you have to project the capabilities of the prospects but also now must project the capabilities of Teheran. Will he be healthy? Will he be as effective? Less? More? You know he will be more costly but still cheap on a relative basis.
When you look at Teheran and project his future 2-3 years from now, you are making an educated guess or bet on what he will be based on the evidence of what he was and his ML stability. To a certain extent the same is being done with the pitching prospects but based on more limited historical information and impacted by unstable growth. So, projecting prospects is more of a gamble than projecting an established ML, but with less monetary downside. You mitigate that through numbers, and the Braves have numbers. So chances are, if the scouts and FO have done good work, then 2-3 years from now the Braves will have 1 or more pitchers just as good or better than Teheran is today and possibly much better than Teheran will be then.
Now, if you believe Teheran will become an ACE, providing huge value because of his performance and rarity, then you gamble by keeping him every time. If you believe, as I do, that he is very unlikely to be any better then than he is now, and potentially much worse, then moving him for the right return is an attractive option.