That you went back to Pronger just highlights how seldom a team trades that kind of talent...
And if you look at what he was traded for, it actually makes my point...
In 05 for Brewer (a top young nhler, 24yr old top pairing D who was a former top 5 pick ), a recent 1st (very similar to Poehling) & recent 2nd
In 06 for luppul (top 6 fwd, recent 7th overall, 23 years old), Smid (top prospect, 2 yrs from 9th overall), a 1st, 2nd & conditional 1st (turned into Eberle).
In 09 for Lupul again (now less valuable but still top 6), 2x 1st, 3rd & top prospect D (sbisa, 1 year from 19th overall).
In none of the cases was a cap burden like Byron included, nor a Ufa to be...
So yeah, your Pronger example amplifies the point that your initial offer was unrealistically low.
Re Larkin/Mantha... I bet Yzerman wouldn't blink if he could turn those two into Crosby... He, better than many GMs, knows just how rare and valuable that kind of talent & leadership is worth.